I'm going to put my in-law in a headlock
Why does your in-law deserve a headlock?
They keep acting out of place
It's okay to not get along with your in-laws, but its wrong to intentionally hurt them. You could possibly be charged for harming them physically.
How else will they learn a lesson?
Talking to them about their behavior is a good start. Starting off with violence will make it less likely they will listen to what you have to say.