The Family Tree

So the deformed Abel and Cain are sons of the Sheriff. But why did he call them brothers and even the grandmother also regarded the grandfather as their daddy too. Did they know themselves are their own brother's sons?

And who is Bruna under John family tree? It was not the same line with Kelly and Briele. It seems like he got children from two different persons. Is Bruna another inbred son/daughter between John and his own mother before he went out of the crazy tradition and then get married to a normal wife?