@normans13,
It sounds to me that you are correct about the "ethics" of the situation. If I were your cousin, I would share this money with you. Unfortunately I don't think that ethics matter one bit in this situation.
This is a legal question. The only important question is what the law says. Hopefully you have talked to a lawyer in your state. If you haven't, then you should.
My two pieces of advice are
1) Talk to a lawyer. In my experience it is good to pay a lawyer one or two hundred bucks for a bit of their time.. this way they will give you advice rather than a sales pitch, and ask them what their opinion is of your chances in court.
2) If the lawyer says you don't have a case, then move on. I might stop sending my cousins Christmas cards... but it really isn't worth much to fret about this. Life isn't always ethical.