It honestly depends how Ronan fights. If he messes around at all and uses some of the stone’s weaker attacks (some of the blasts Thanos used in IW) and lets Thanos close in, he’s done. If he goes straight for the planet bust or something close to that, he wins.
1. Cap wins eventually. Oliver could possibly win if he gets lucky or used the scepter.
2. Probably does somewhat well like Cap did for a short bit, but one hit from Thanos would probably kill him or severely injure him (take him completely out of the fight). He wouldn’t be able to take the damage that Cap did or even close.