Do you think that them not complaining about each other to you would stop your anxiety on whether the house is holding up? Since you still have awareness of how your wife/parents feel about each other, and perhaps things that have happened between them?

Iout of curiosity, why are they still living together if they find each other intolerable? It doesn't sound like an enjoyable environment for anyone involved. It seems like living in seperate households is something to consider, if it's able to happen. Or maybe.. some family therapy?

In the meantime, perhaps you can speak to each of them about how the conflict is affecting your work? Them venting to you doesn't necessarily have to stop, but it could simply be lessened. However, it depends on what you can tolerate. So if thats no venting to you at all, then that's the boundary you set.

Im not sure how I would word it, Maybe something like, "the conflict has been taking its toll on me to the point of my boss noticing a decline in my performance, i'd appreciate it if we would spend less time conversing about the situation at home"? Just something to give you an idea if you were to set your boundary and you needed help with how you would say it.