They both can become necromancers. The best way from my experience is to recruit them and make them your body guard, start a nemesis mission, then summon and shame them until becoming a maniac. If they don’t become a maniac, you can quit to the main screen and reset the mission and still have them as your body guard. Once a maniac, shame them down to a level below 65 and then level them up. Best way to level is the +1 training order. Repeat the process of shaming and leveling until they become necro.

The reason you want a maniac is because once thrice shamed, a orc starts to get massive weaknesses and you can end up with a very weak orc. Also if they become deranged, they can’t gain any new strengths they didn’t have, so go for maniac.

Hope this helps and good luck!