On Imdb it says in godfather 3 there was a character called Leo Cuneo he's the character who gets shot and calls zaza a son of a bitch. Is he a relation to the Cuneo family?

The guy who calls Zasa a son of a bitch is, if I recall correctly, Carmine Caridi, who played "Albert Volpe." He played Carmine Rosato in II. "Leo Cuneo" may or may not have been intended to be a descendent of "Carmine Cuneo" who was whacked in GF.

Which one was Carmine Cuneo in GF I? Was he the bad guy fixing his comb over at the commission meeting?

The guy with the comb was Tattaglia. Carmine Cuneo was the next to last guy Vito introduced.

Combover man is Tattaglia. He refers to his son being killed in the meeting. Tessio - "we hit Bruno Tattaglia at 4 in the morning".

Cuneo I believe is the guy with the dark hair and pencil thin mustache who Willie Cicci kills in the revolving door. When Vito is acknowledging/thanking the members who came to the meeting, the camera pans the table. As Vito says a name, the camera pans the individuals fairly close to the introduction. At least that is the way I took it.