Good question.

Probably not. Michael told Kay he was distanced from his family, as in "That's my family, Kay--it's not me." That was enough for her. I doubt she'd have married him, after Sicily, if he admitted he'd killed Mac and Sol. He had always denied it.

I was always struck by a cultural difference between Sicily and the US. When Michael meets Sr. Vitelli, he says he's "an American hiding from the police of mycountry." Vitelli accepts that without blinking because in Sicily at that time, the authorities were regarded as foes. If Michael were wooing an American girl and said that to her father, he'd probably turn Michael in to the cops.