My interpretation of the ending

You´re right, that didn´t make a lot of sense. I don´t think Rosa Maria was given for adoption. It´s more likely that the italian family just didn´t care very much for her because she wasn´t really the daughter of gianni´s father, as gianni´s mother says.

I think the whole movie was too slow and the grim atmosphere the director wanted to create didn´t work. Sophie Marceu´s perfomance was much better than Monica Bellucci`s: the italian lady, though stunning as usual, seemed stiff. Kind of a disappointment.

I got an idea of what might have happened, but i got the same unanswered questions as you do.

So.. the 2 girls at the age of 8 were childhood friends and one day, on a road trip with the french family, the french girl (the blonde one, Jeanne) was killed in an accident. Ever since, the italian girl (Rosa Maria) lost her memory and comfused her life with the life of Jeanne (possibly from a post traumatic shock). She begged the french mom to raise her since she thought she was Jeanne, and so the french mom did (another person with a post traumatic shock who couldnt come to terms with the loss of their own child). That's why her memory as Sophie Marceau is non existent before her 8th year of age and she can't remember anything. I guess the italian family never got aware of that and thought their daughter was the one that got killed, that's the reason they said Rosa Maria as Belucci couldn't be alive because she was dead. However, as the years passed by, and while she was trying to find out about her childhood (that was the action that triggered the whole revelation), Rosa Maria started having flashes from reality, waking her from her long-term illusion state, and slowly discovered she was not Jeanne, but Rosa Maria instead. My interpretation of the ending was that she finally came to terms with the loss of her childhood friend, and pretended she was near her, feeling her still close, giving her the inspiration she needed.

My unanswered questions were, how in the world could she "visualize" her own brother's face so perfectly, without having seen him in his present age.. ok, i get it about her true mom, but her brother.. that doesnt make sense. Also, the kids.. why were they different?

Sophie was adopted by the French woman because her mother chooses her husband over a bastard daughter. We cannot know why the French woman, although already being the mother of one girl, decided to take the Italian girl to home, but this isn’t the point of the film. At some point in her early life, she survives a car clash that takes the life of her adoptive sister. The French woman leads her to believe she could replace her legitimate daughter. And she spent the last years of her childhood and adolescence like this, growing up believing she was truly her daughter. When she starts to write her memories, she felts some things didn’t join together and her crisis starts. To me the ending was a symbol of a woman knowing her past, forgiving her mother and trying to build an identity to herself from all that she lived upon that moment.

"Something's uncertain, still: why did Jeanne's "fake" life (in which she's played by Sophie Marceau) contain Rosa-Maria's brother as her husband? And why did her children change too?"

I think her mind is reaching for anything familar to anchor the new perception of reality too. Her mind used what it thought her brother would look like as an adult for this template. It just so happens her mind was correct in how her brother would look like. Not at all out of the realm of possiblity. Her mother may have many times that her baby brother looked like thier dad and Rosa's mind uses that to construct the adult brother.

Why did the children change...My guess is she was imposing how Jeanne looked as a child on her children. As such when the change happened they started to look like her instead of how she remembered Jeanne.

"I'm not sure I understand which action triggered the personality-clash between her two "sides" and start the "transformation"."

The whole event is triggered when she becomes so wrapped up in the details of her childhood. Her mind is trying to unravel the memories of Rosa from the memories of Jeanne.

I have seen others ask why the strange arm movements in the reflections. My guess is this one of the girlhood games she and Jeanne would play...kind of like how children play the repeat game or the hand clapping games. The reflections were merely the first attempt her mind was using to try and unravel rosa from Jeanne.

I have also seen the questions of why the blisters on the arm and why the distortion of rosa's body after looking in the mirror in the italian house.
My guess is she knew she was going crazy. She knew there were 2 of her. To rationalize this her mind made it seem that her body was splitting into two.

Spoilers ahead:

Rosa Maria (the Italian girl) was given over to Jeanine's (the French girl) family. Perhaps mama had an affair and because she was rejected by her mother's husband because she was not his, the mother decided to give her up. This is Italy after all.

While driving with the new family to their home and a new life, they have an accident. Jeanine dies and apparently, her new mom's husband dies. She has no memory of her previous life and for whatever reason begs her new mom to call her Jeannine. The new mom missing her own daughter begins calling Rosa Marie by her dead daughter's name. The new Jeannine over the years has asked her mom a lot of questions about her early life. The answers apparently never satisfy her.

As an adult, something begins to trigger her memory. It may be a car accident that she witnesses or sees the aftermath of at the beginning of the movie. Maybe it was her editor telling her, her attempt at writing an autobiography was boring and awful. She sees changes in herself, husband, her family, her mother, her surrounds, and at times sees a little dark-haired girl (her real self).

In the end she realizes she had been living the imagined life of the real Jeanine if she had lived. In reality she began to see her real life husband and children and self. At the end she accepts the "ghost" of her past and the imagined life of the dead girl had she lived. With the ending showing her real self and the long-dead girl (now an adult in her mind) typing a story side by side, the assumption would be she can now be able to write an autobiography with her recovered memories of who she really is.

Everything is in the perception of Jeanne.
She thinks she knows nothing before she was eight.
The fact is she subconsciously knows a lot.
She has worked upon a book which is not a biography (she is good at biography) and it is fiction. But in attempting to create fiction she finds it cold and her writing is bad. Because she is trying to create her mind is now attempting to go back into a past she has forgotten.
Everything at first is just her perception of what she is. It is a mixture of what she really is and what she imagines herself to be.
She thinks she is going mad but what is happening is her real childhood starts interfering with her real life and that is what you see as everything and everyone distorts.
The Italian sequence is where we learn what really happened and why it has a traumatic effect when it start resurging. Her mother has an affair. Her mother's husband hates the bastard. Some French tourists/ friends agree to take the kid and she makes friends with the new parent's daughter, Jeanne.
They are very close but are ripped apart by the crash. The trauma makes Rosa- Marie, so entranced by Jeanne, assume her persona in her mind and she keeps this up into her marriage, until the time the film starts and it is all falling apart.
Note how Rosa-Marie becomes the little girl again in her own perception as she grapples with the understanding of what happened.
The reunion in the appartment is a bit of a trick by the director which really will put people off and confuse them.
It is Rosa-Marie who comes back to the appartment but the Director inserts the real Jeanne for an effect. Also you see Rosa-Marie acknowledge the figment Jeanne as she goes into the bedroom to see her children.
The last shot, that of them typing, is Rosa-Marie now at one with Jeanne, writing the fiction and story of,possibly their tale,but more likely a fictionalised account with far more depth, warmth and clarity than the first attempt.
If you understand that everything in this film is Rosa-Marie's perception of herself as the film progresses it might become easier to comprehend.
Anyway, that's my take.

After the accident, Rosa-Maria identified with and kept living as Jeanne. However, her subconscious still retained the information about who she really was, and when this information began to surface, Jeanne began to loose grip on reality and to doubt her mental sanity. When - in the end - she understood everything, she managed to assimilate both personas, a little bit like how a person with multiple identity disorder manages to integrate all personalities. However, Jeanne could not create a new persona or choose between the already existing two, but they kept living side by side in her (my interpretation of the ending with Jeanne and Rosa-Maria writing together). I don't think that is really possible, so I took it as an artistic license.

Artistic license is also my answer to your first two questions (Maria Rosa's brother as Jeanne's husband and the changing kids).

The transformation was caused by Jeanne's foray into childhood memories for her book.

An interesting aspect is that I believe that such a major trauma after the accident (loosing one's sense of identity) must have had a physical representation in the brain, which would have become apparent through detailed medical investigation (brain scan).

What confused me was her kids changing... She saw them as more dark haired and dark featured than they really were, but if she really thought of herself as Jeanne, wouldn't it have been the opposite (as in, shouldn't they have changed to more Italian looking when she figured out her past)?

Life's a bitch, but god forbid the bitch divorce me