If she's a gold digger, have words with her, to let them know, that you know what's going on... then walk away
If things are not OK now, they certainly wont be in the future, and the welfare of the In laws are the priority!
We had a very similar situation few years back, that in retrospect, had their been discussion, it would have solved many problems. The family is now totally divided on my wife's side, with zero chance of any reconciliation, we've had to start again from scratch!
Thom