Sometimes with family (mine anyway) you just can't talk about it.
You can explain until your blue in the face then they just go and do what they like when your back is turned.

What do I do?
Avoid, aviod, avoid!!

WW3 just isn't worth it in the long run.
Just limit your contact and avoid them as much as humanly possible!!
I also moved 1500km between each side of the family