Is that true that her siblings have said that? I knew about her mother, but from what little I could gather it sounded like her mom has a lot of issues.
In the era we live in I think that it's hard for people to understand that we still don't know very much about what happened. This really is a he said/she said situation. He comes across as a not very likable individual (to put it mildly), but that doesn't mean that he was actually physically abusing her. If her family says that she's making it up, that's troubling.
When I was in college I had an acquaintance that I admired who committed suicide. The police had picked him up and booked him on rape charges, and they leaned pretty hard on him trying to get him to confess to it. He played football and had a squeaky clean reputation, pretty much admired by all. That was what they went after, trying to get him to confess so that he wouldn't get the book thrown at him. He was so frightened and ashamed that he went out and shot himself. Afterward, the girl admitted that she had made it up because her father had seen hickies on her. She was 18 years old, still living at home, and she was too frightened to tell her father the truth, that she had been more than willing. The guy's family is still devastated nearly three decades later, and that's not the sort of thing that you ever put behind you. I've often wondered what ever happened to her. That would be quite a burden to carry for the rest of your life.
I think about that when stories like this one come out. Zach Smith might very well be a spouse abuser,... but he might not. Looking at his Twitter rampage, I am concerned that he's going to hurt himself. Imagine being in his situation without having done what you're accused of doing. I don't know how I'd respond, but I wouldn't wish that on my worst enemy.