Hearns is just nightmarish for Floyd. Floyd would have the fight of his life just trying to box with him. Hearns would be able to keep Floyd at bay with his reach and his known power. Floyd can sort of turn into a pressure fighter like he did against Judah after getting outboxed but Judah is not Hearns. Floyd doesn't have the size nor the agression to impose himself on Hearns and would probably eventually get clipped trying.
Hearns by decision. Would expect it to be similar to Hearns vs. Benitez which was a masterpiece of a boxing match.
Mayweather doesn't have the power to get anything going against Tommy. At best he loses a decision. But he more than likely gets stopped.
Hearns knocks Floyd out in the second round, Roger in the third and lastly Floyd Sr. in the fourth. Though i am not so sure, he probably could knock both Roger and Floyd Sr. in the third if he pressed.
Hearns will be difficult then again Hearns is difficult for everyone in history at Welterweight. 15 rounds might suit Floyd in this one.