Problems with partners family

My partner is very close to her family. Her father passed away early last year and I am just trying to be supportive. With her father gone we have spent a lot more time with her sister and her partner. 

This is now causing me some stress because of comments her sister but mainly her partner has said towards me and is overall rude. He is a moaner so my partner said she doesn't really listen to him. 

One time he was complaining and he basically took the man's side in some abuse case that was on the news and I said funny how you take his side yet you have no idea what's gone on. He went mad and was shouting at me. He shouted to my partner's sister "SARAH IF THIS HAPPENED TO YOU WOULD YOU TELL THEM TO STOP YES OR NO?" She just said yes and he carried on shouting basically an I told you so situation and he was so aggressive towards me in the way he spoke. I am absolutely shocked still that everyone in the room just sat there and let him speak to me like that. My partner, her mum and her sister... 

When he was shouting I didn't know what to do, so I tried to discreetly poke my partner but she just turned and looked at me and smiled like why you poking me. I just felt humiliated. I wanted to get up and walk out but I feel I can't at their house because they have dogs (they haven't trained them properly) they go mad if you get up especially towards the door, plus our shoes are put in the cupboard (because of the dogs) so walking out would be a long process. I feel trapped there sometimes. 

I have spoken to my partner but she said like before that she doesn't really listen to what he's saying because he moans all the time but I can't get over the way he spoke to me and no one doing anything at all. I can't seem to stop going over it in my head and thinking how could my partner not see how horrible he was. This is really bothering me because I love her more than anything but I just can't understand why she didn't react.

I keep going over this situation and other times her family have been rude towards me and I'm struggling to let it go because I always bite my tongue. The situation I've described has been the worst time something like this has happened and I can't stop going over it in my head. I've had trouble sleeping over it too, I feel like I'm going mad.