I don't like to hang out with my girlfriend's family every week, what do I say to her or am I just an ass?

I'm 23m my girlfriend is 21, her family lives about 30 minutes away while mine lives several hours away in another state. At least once a week, she gets invited to go out to dinner or their house and she invites me to go with her. I don't mind doing dinner or lunch every once in a while but it almost always turns into a 4+ hour event. Everyone in their family is afraid of the Dad, a lot of things happen without him knowing because they are afraid of what he will do. He has tried to use me to embarrass his own son to the point of his son crying(with some kind of pictures, he's not a pedo or anything but I don't know what they were) Instead of anyone calling the Dad out for being out of line, they just told the son to do what the dad wanted. To but it bluntly, that p*ssed me off and I found it very disturbing that he would do that to his own son and how silent and obedient the family was, not even his wife stood up for the son. I don't think he does any physical harm to anyone but there must be some kind of verbal/emotional consequence they are afraid of. My father would never do that me and if he crossed the line that far someone would have stepped in. I didn't... I'm not sure what the right thing to do was, but I don't think a boyfriends say will do anybody any good. One of her sisters has a mental disability which I know is nobodies fault, but they encourage her to sing at the top of her lungs and act wild at restaurants and dinner and then they think its cute and sometimes have her do another song. The singing is pretty bad to say the least and it really does get to my nerves to hear it but the fact that they encourage that behavior (I know I shouldn't judge on how to raise their children again, but come on there is a time and a place for that and I'm pretty sure it isn't at restaurant.)

All this added up is pretty taxing for me, afterwards I feel drained from just trying to sit through it and act like none of it bothers me. I really don't like seeing them every week because of it.

Do I tell my girlfriend all this? I know she will get offended about the part about her sister and probably ashamed about her dad.

Should I just make excuses not go? I can put up with it to a degree, but not every week.

What would you do? Or am I just being inconsiderate?
+1 y
Thought I should add, it's not just those two reasons I mentioned. Similar things happen every time that always create a really awkward situation. When the Dad doesn't go it's usually not as bad. Her family is nice to me, I am respectful, but its hard.
I don't like to hang out with my girlfriend's family every week, what do I say to her or am I just an ass?
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