MIL weird relationship with my bf?

I'm pretty embarrassed that this bothers me but I feel like my bf relationship with his mom is weird n it kind of pisses me off sometimes. His mom "plays around" sometimes n reaches 'down there' at his son when he's not looking then she laughs and it gets all awkward. For example I came over my bfs house and we were watching tv at the couch, he had some basketball shorts on then his mom came in the house from work and she said hi to him and he said hi back and she literally reach up from his leg into his basketball shorts! My bf got so red and flinched real hard and she laughed. She did this twice and I had to look away cus it was so awkward. When she walked away I asked him what was she trying to do (I was acting stupid) and he said "she was trying to grab me down there! I'm telling u she's crazy" then I told him wtf don't let her do that. This happen again in a different occasion. This was months ago when I was pregnant, sometimes she says some real stupid sexual stuff and it annoys me. Yesterday his mom called me which she never does and told me her life story about her and husband and how her husband treated her wrong the first few years together after having their son. (Me and my bf are having problems and I was thinking of breaking up) she was practically telling me to stick things through with her son and things will get better. Then she went off and off about how much of a good relationship she has with her son and how much they talk even about sex (she said this twice in the convo) and that she's open about talking about sex with him..My bf has also talked about his mom before and would make comments like "my mom has some big thighs" or irrelevant things. His uncle made a comment about how our baby is going to be "sexy" growing up and it really bothered me. Who thinks about stuff like that? My bf told me once that he's worry about the boys talking to her and if she's anything like me she's going to have really big boobs. I don't know if I'm really OVER thinking all this or if his family are really open sexual people who just think about sexual stuff but all this puts me on a bad side. I'm thinking about everything his mom told me yesterday and I want to ask my bf what kind of things they talk about since she's so comfortable about talking sex with him. What about sex? He's 21 and im 22 wtf does she have to talk to him about? I'm not sure if i should bring any of this up and if so how?

*My sister and best friend said the same thing about sexual abuse and that was two separate conversations I had with them. It really creeped me out and scared me. I have my baby now she's 3 weeks old and im scared scared to leave her alone with any of them.