I have two SILs that absolutely does not get along with my MIL or the family.
For me I get along great with my MIL and in laws. Why? Because for me I don't care what my MIL think of me. I'm confident, I don't need anyone's approval and I believe people are entitled to not like me, even my MIL. I don't engage in argument with my MIL. I don't complain or b.tch about what my MIL does, don't do, say do say to one nyab versa me, how she treats the other grandkids compare to my kids. And when my MIL asked me to do something I cannot do, I am honest with her and tell her I can't do it and if that makes me a bad person, I will bare that name. I also don't go complain and b.tich to my parents about what my MIL is doing, isn't doing for me , to me. I leave my MIL alone. And when she yells at my husband for something, I don't intervene. She can yell at her son all she wants. It's between them. And when there's gossip that my MIL is saying this or that about me, I don't care nor bring it up. But if my MIL brings it up, I tell her " Its okay. Whether you have said or not, it doesn't matter to me." and simply mean it and continue to treat her the same as everyday. I never share with my parents about what goes on with my MIL so my MIL and parents are on good term. Over time she came to like me a lot and stop giving me dirty looks. lol
Why the other SILs don't get along with her, or why the family doesn't like them? Well, first they bit.ch and complain to their husbands and my MIL about every little thing my MIL isn't doing, or doing to them that isn't fair or is hurtful. They also go tell their parents about everything that goes on. Than their parents wants to take my MIL to Hmong court and there is tension between my MIL and their parents. They cry fowl and always so dam hurt by everything. They call me MIL out for some shi.t that isn't even worth it. These SILs are so dumb, they don't know how to pick their battles. They just fight even battles that isn't even worth fighting lol. They want to have a good relationship with their husband's sisters and brothers, but they fail to understand that their relationship with the sisters and brothers are dependent on their relationship with their MIL because my MIL's daughters and most sons are very protective of her and has a good relationship with her.