Elyse is a really good unit that will carry you far (her skill is really OP), however in the immediate, your range dps needs a lot of work, so I would focus on Bashira first. Getting her CCed and leveled should be the highest priority, IMO. After that you can go back for Elyse. Altia I would put much lower on the list since Katie should be fine for the time being.

As for Necromancers... they are generally a niche unit that specializes in summoning tokens, which has some uses, mostly to stall bosses. Luckily, Agnes is more damage focus, and should help a lot in phalanx 2 if you're still having trouble with it since she can hit 3 enemies on skill and doesn't need to be CCed (although she's slow compared to witches). Just toss some quick early levels on her, and she should make that map fairly simple.