Question

When Jimmy was declared legally dead they no longer had any relation whatsoever. Before when he lived had Tommy and Sheila done anything they would have broken no laws except for maybe adultery which is a misdemeanor in most of the few states with a law still on the books. Not sure if NY still has one.

So no, there was no incest nor potential incest. She married into his family and was abandoned by it, notice the rest never really checked up on her or her son after her husband died in the line of duty.

Incest only applies to blood relatives