So you are both stupid, “oooooh he’s my relative, he’s free to victimize society, I would do anything to stop him”.
Please say dumb not stupid. You can’t fix stupid.
If a loved one openly bragged about his criminal activity, that means that I have failed as a parent or uncle.
And I don’t want to fail.
And the above failure is years in the making, not a spontaneous spark of “Hey, Ima gonna break into 200 cars”.
So yes, I’d turn them in, because it would mean they ignored my guidance, and are thus dead to me.