Until you have found the way to do what you plan at home, get much strength from your brother.
Tell him everything you can. Let him be an ally. You could even use him as a reason to
step aside (as far as wife is concerned- don't use him with the elder body- too easy to recommend
a DF).
I was a bit heavy, but it might get through better. You watch R rated movies with the daughter and
mention Karate? Good for you. Be sure to encourage lots of education. Perhaps ask the kids
if shunning their uncle is the right thing to do. What would they do in YOUR situation? If you did
contact their uncle, what would MOM say? Should we keep it a secret? Just some stray thoughts.