Give up. My in laws are the same and it took me 4 years of feeling on edge and like shit to just give up. I couldn't understand how I was able to get along really well and chat away really easily with just about anyone but them.
Then SiL had her wedding last month. One of my DPs other sisters came up for it, and brought her partner. I get on really well with him but once we'd chatted for an hour or two, he basically then just clammed up for the rest of the night and my in laws were acting like he was being a dick. But it hit me: it's because nobody ever makes an effort with him, it's all one way.
This SiL has an 18 year old son, and he had brought his girlfriend to the wedding. She was lovely, really chatty and nice girl. Same thing happened with her. I danced with her for a bit, we talked, and then I noticed nobody bothered with her. She was sitting there at the table and SiL (so her "MiL") didnt so much as look at her. Nor did my MiL.
I realised that night that it wasnt fucking me at all. The only warm and engaging people I ever seem to meet at these gatherings are the "plus ones", not the actual family. I wont be going to any more family events. It chips away at your soul a little bit. With this last event, like you I got the sense that some story about me was doing the rounds.
Sorry for the ramble, but just to let you know: you arent alone, and life is too short.