If I were Reem i'd be diving for Roy's shoelaces first chance I get otherwise I'll be diving for his shoelaces anyway but with the conscious intention to do anyway.
Reem has good skills everywhere but on paper, Roy is a bad match for him purely because Reem can't take a shot and Nelson can. Reem has to either pour on an early attack that gets Roy out of there, execute a very smart gameplan on Roy a la Mir and do so with patience and commitment.
Nelson brings his power and his chin. Reem can put him down because Reem does have a lot of power but if we are talking about who is more likely to get stopped, we gotta say it's Reem. Tough fight but I think it favors Nelson.