How does one stop feeling sorry for themselves?

I have inlaw issues and it is driving me nuts (seriously a mental institution would be great, no kidding either) and they actually make me look and sound crazy, I am 32yo and they treat me like I am a child (which makes me want to behave like one to retaliate) and even though I am a parent of 3 kids they take over and parent my children right in front of me, I say no lollies because it is nearly a meal time, you can have lollies after, they say quietly "go hide in the hall and eat these lollies before Mum sees you". I actually have ears and can hear them say this and they think it is hilarious, so my children wont listen to a word I say when ever my in laws are around. Geez help me, I seriously want to cut all contact with them but it would hurt my partner and his Mum, what do I do?