Two Questions: Why Don't Sisters Talk to Grandmother, Suzu's Family Name

It appears as if the Grandmother lives nearby, since her funeral is in this town, but the sisters have no contact with her. Instead, they have a nice relationship with her sister, "Great Auntie."

I believe this is explained by a couple of lines of dialogue which I couldn't make sense of, perhaps because of a bad translation. I wish I'd written them down precisely, but it involved there not being a divorce*, the Grandmother not allowing something or other, and this happening "because of us." So it seems as if the sisters and Grandmother may have had a falling-out over this. And hence don't speak.

*I'm also wondering why Suzu has a different family name than her sisters ... is Asano actually her mother's family name because her parents were not legally married because her Dad was not legally divorced from the sister's Mom? In which case when the sisters refer to Suzu's mother Yoko as the "third wife," the word for wife couldn't mean legal wife.

Prepare your minds for a new scale of physical, scientific values, gentlemen.