This is so sticky, isn't it??? There is not much you can do when they go behind your back to talk to the teacher - the teacher needs to handle this. It's already mid-April, so perhaps you should just finish out the year, but then maybe you can get your child in another class in the future - speak to the teacher or the director of the school. Same thing if they go to the same public school. Parents do this all the time - you can't choose the teacher, but you CAN do things like separate twins or cousins. Don't engage the inlaws with this, just do it with the school. Have you already engaged them in some way to discuss prior episodes and comments they have made in your presence? If others are telling you that the BIL and wife have complaints, then you perhaps should say "I'm sorry if they bothered you with this, but they haven't said anything to us." Then stop discussing it with others saying, "I really can't do anything about this through a third party" or "...unless they speak with us directly." If any complaints occur to your face, you might try saying that you are sorry they are unhappy, and then removing your children from the interactions with the cousins, and going home. This will end the problem one way or another - either they will get the message and stop complaining, or you will at least go home and avoid the stress. The purpose of family get-togethers is to share and enjoy - if it's not pleasant or, even worse, if it is hostile, you need to remove yourselves and your children from that environment. And that is all you should say - "Since this is upsetting you, let's call it a day." Or, "We really want our children to enjoy the time with their cousins, and this criticism upsets them and colors their relationships. So let's get together another time when everyone's feeling better." Then leave. Everyone has to parent their children the way they feel is best, and you can certainly "have it out" with the adults without the children being present - if you think it will do any good. If it won't, then all you can do is leave pleasantly but firmly. Every time. Either their behavior will change, or you will be removed from it. Tell your kids up front that Uncle and Aunt love them but that short visits are best, and that you will visit often but for shorter periods of time. If the criticism is of your children directly, then definitely remove them if there is no justification for it. Tell your relatives to tell YOU if there is a problem and not to discipline your kids. You weren't really specific about the kinds of things they say, so that's why I am suggesting different things. But I can tell you that allowing this to continue after 7 years isn't working!