you dont!
Yes, you do. You just dont do it openly so it doesnt look like a fight.
Stop arguing with your husband
Stop arguing with you MIL
Stop letting them get to you because that is exactly what they want! They want you to lose it, get angry and then go tell your husband how mean you are
I know its easier said then done but you HAVE to start being nice to your MIL, SIL and BIL. The reason is not because you should but because you cant give them any reason to come at you.
Your goal is to take away any and all reasons for them to complain. Two things will happen:
They might be so touched by your kindness they stop destroying your life
They might feel like idiots complaining about you to your husband because you are as close to perfect as a bahu can get!
This sounds so easy but its much harder to do. But if you can do it...kudos to you.