[sammyg2]

Who does ther violin belong to?
Did grandpa give it to the wife to play, or to own?
If the MIL gave it to someone else, then clearly the wife did not own it and had no claim to it. It was mearly loaned to her.
Technically it belonged to the MIL (inhereted from her husband or joint property, whichever), and she gave it to the SIL.
Same question, was that give it to play or give it to own?

If the MIL gave it to the SIL to own, then it belongs to her. If she merely LOANED it to hte SIl for her kid to play, then it still belongs to the mIL.
Is she still around? if not it goes to probate and the SIL keeps it.
What you are planning to do is sneaky and borderline dishonest. You are trying to trick someone out of it, to CON it away even though you have no legal claim to it.

My conscience would not allow me to pull something like that.
You have to look yourself in the mirror. Are you OK with donig things like that, is that the type of person you are OK with being?

If I were you and you're glad I'm not, I'd go buy my daughter an instrument equal to her talent and move on.