Lets say the brother thing doesn't apply to either one holding back and they're both giving it their all. Who has what advantage? I definitely think Vitali has a better chin, for starters.
I can not recall a high level match between brothers. Family should become before sport. It would be a wired if the two ever fought, and likely a stinker of an outcome. If the two were not related, the match would be a highly anticipated show down. I think Vitlai would eventually break though Wlads defenses and score a TKO.