Regroup, buddy, regroup. Focus on the type of person you want to be - no doubt this will be the hardest thing you ever do, but you have got to let this situation go and 1) focus hard on your relationship with Christ 2) Tell Jesus you need help being the person you want to be 3) Treat W the way you would like to be able to treat her.
You will only be able to do #3 with God's help. She will spit in your face - maybe even literally, but you must treat W as if you had accomplished the R you want. That is DBing. You have to do things you don't want to, you shouldn't have to, that you honestly can't do. You have done so well, and put up with so much.
Jesus is just waiting for you to give up so he can carry this burden for you. It is the hardest thing I have ever done, but also the absolute best after it was done, for me and my R.
Doesn't sound like you are at a boiling point, just W is. Be the person you want to be - include W in that and show her how good your R can be again.
Douse the flame with FIL by only listening - damage may already be done, but I think he may be Ws pressure valve right now. Let W and FIL have relationship and vent to each other, you are already in the middle, just be cool and let the storm whip around you.
I take W's concern about retaining a L a good sign, VALIDATE that you want to work with W. Not sure telling her to do what she's got to do is best comeback anymore.
I used, "I'm not going to tell you what to do", but my W's issue was me controlling her.
