Is your deceased uncle's wife related to you?

Your aunt (sister of one of your parents) and her husband were your aunt and uncle, particularly if he is the father of some of your cousins. If he is still acting as a member of your family, and accepted by you and others in your family, then he is still your uncle.

While his new wife is not technically related to you at all, most families will probably treat her as your aunt, and he may well expect that too. Of course, being a relative does not mean you have to like the person. That is an entirely different matter.