Is there a way to make NPC's from the citizens plugin cast spells to attack, like using the sentinel trait but with magic instead of normal weapons?

Sentinel NPCs can cast spells in the current dev build, slated to be released as 7.5.3

.. Didn't quite make it in under a year, but better late then never, amirite?

No, I'm afraid not. I can keep this open as a feature request if you like.

Your best bet in the meantime is to use Magic Mobs (see wiki) or MythicMobs, though the last time I tried that their command skill didn't seem to work anymore, so maybe not.

Yes that'd be good thank you :)