Does anyone else not get along with S/Os family, but the relationship still works?

My boyfriends sister talking crap about him calling him fat.

Me and my boyfriend are very similar personalities. Hes the youngest of his siblings and hes a bit older than i am. I was talking with him and his sister for the first time yesterday at the table and his talkative sister kept calling him fat throughout the few hours. Like “omg your arms are so fat” or calling him “gordo” i felt bad and my boyfriend is super insecure about his body. And i could see how uncomfortable he was and probably embarrassed. He is 5’11 and hes not even that big. His belly isnt sticking out or anything like that. But either way, i dont like how his family talks down on each other and make hurtful jokes. Some can be funny, but it also is kind of toxic.

He said its the way his family had always been. I dont mind a few jokes but not just straight up calling someone fat. My family is pretty skinny, so am i and my family isnt as close knit but we also do not put each other down like that. We lift each other up. She was even talking down on her 18 year old daughter saying her clothes are ugly and she doesnt take care of herself. But like… she raised her. She also said, “i wouldnt have kids with him youre gonna have fat babies. Your poor stomach is gonna stretch” Ive already had a baby, and i have 0 stretch marks from it and i have good genes. His sister was once over 300 pounds but lost a lot of weight. And is a bit smaller now, but still is unhealthy and while they laugh and joke a lot she still talks down on him. What if i do end up having a kid with him and shes the aunt? Why would i want my baby to have an aunt judging my childs weight? Thats not at all how i raise my current child, or how i would want to raise any future children.

All this to say, but i had a fine conversation with her and we get along, but i dont agree with some of how his family acts. Hes kind of like the quiet black sheep of the family and so am i, so we sort of have that in common.