E.T.
This is your husband's fight. He needs to stand up to his parents/sisters and tell them that they MUST treat you with respect and must be fair to the children you have together, or else your family will not be able to spend time with them. It's as simple as that.
If you took out the word "in laws" and replaced it with "friends", you will easily realize you wouldn't continue a relationship with friends who refused to speak to you (but spoke to your husband), treated your kids poorly, or made anyone in your family uncomfortable. So why are you accepting this from in laws? You are showing your children that mommy can be treated badly, and so can they. That is not a lesson they need.
I'm sure it will be hard, but your husband needs to speak up and deal with this with his parents.