Am I the arse whole for wanting nothing to do with my girlfriends mum and stepdad

My girlfriend, 23w had an awful upbringing. Her stepdad is a narcissist. He would bully her, physically abuse her and her mother when she was younger from the ages of around 11-17.

When she got a little bit older she realised that he also sexually abused her.

She lives 3 hours away from them now, her mother and step dad have 2 children of there own.

At the time her mother didn't believe her, the stepdad is upper class and job involves contracting for the police.

I was skeptical about meeting them, I met her mother 6 months after dating for around an hour which was fine. Then met the whole family after a year and a half. It is extremely uncomfortable knowing what has happened and simply been brushed under the carpet the carpet. Each conversation feels like and act I want to beat the living shit out of the stepdad.

My girlfriend deeply wants a relationship with her mother, despite from what I have seen her mother doing very little to support and be there for her other than occasional financial support but very rarely. Her mother is also controlled somewhat by her stepdad.

The majority of the stepdads family no longer speak to him (they do not know what he has actually done) which speaks to his character and he tore a wedge between but gf mum and sister.

My girlfriend wanted me to visit them over the Christmas holidays, I was in a bad place and did not feel up for the charade and did not go which she was angry with.

Since she told me at the beginning of our relationship I think about it a lot. She has just asked me to go for 2 nights at the end of April.

I just don't think I can be in the same room as this man again. I told my girlfriend I don't want anything to do with him. Of course she doesn't either but feels it's the only way to have a relationship with her mum.

I've suggested talking properly to her mum about everyone that happened and that she can't be around him. But she fears her mum will choose him and have nothing to do with her which in all honesty I could see happening.

I just don't think I can be around this man again without punching him in his smug face