In love but shouldn't be?:
I really feel for you, thats a tough situation.
Are you sure that you are really in love with him, as you only said that you believe you are in love with him. Be careful not to confuse other feelings for love.
Did you know he was your uncle before you got involved?
I know you fall in love with who you fall in love with but there is a brief window in which you can apply the breaks.
What about the other woman he is with? Has he spoken to her yet?
If I were you, I would try to steer clear and if he manages to end the relationship with the other lady and keep his relationship with the kids maybe you could think about him again.

I don't know about the law and deformities. I would say no to both questions, but just think of the people involved in this tangled web and how your decisions will effect them

Its tough I know.

Good luck.