In terms of a boss battle, the succubus could be a magic user and the incubus could be a fighter. I mean typically women are magic users and men are fighters. Most of the cannon women in the series are magic users where as most of the men seem to be fighters. Ok, the belmonts and Alucard may wield magic, but for the most part, they rely heavily on weapon attacks. Then again, both the succubus and incubus could use both magical and physical attacks, but only one at a time. In other words, one would charge in with a physical attack while the other covers them with a magical attack.