From what you described, I don't really see a problem for you or your wife, since it sounds like your MIL pretty much leaves you two alone. Your SIL OTOH sounds like she NEEDS your MIL's interference to avoid going further down the drain, and be glad it's HER taking care of that situation and not you and your wife (until later-on, be prepared). As for your FIL, it's sucks for him, but it's a situation he allowed himself to be put into a long time ago. His options are to get a divorce, commit suicide, or deal with what he's been given. All you can do is offer support.