Scared about my future mother in law.?

[Bubbles]

My future mother in law nit pics my sister in law parenting style. She is consistently telling me things that she doesn't agree with and she shouldn't do this and she should do that. These two women definitely have a strained relationship yet they do make an effort in front of each other yet as soon as my future sister in law's head is turned my future mother in law will jump at the chance to b**ch behind her back. I would hate to hear what she will say when i have kids. I try not to get involved yet i'm sick of just sitting their and not saying anything. Should i say something or just let her b**ch. Or should i say something so it sets a pretance for when i have kids. I would love her advice yet i know we are not going to agree with everything