Have a lot of questions, I’m so lost 😅

Ok, for starters, I’ve been relying quite literally on Nyx for everything. I’ve got her maxed out (except for ascended).

My questions are as follows:

What exactly does Shamir do? What is he good for? My understanding is he’s very similar to Laseer, except I think he’s single target only?

How does Ferssi work? Should I replace Hollow for him, use him in conjuncture? Or replace Dolores? I understand Dolores isn’t a healer, and she’s just there for her buff (A3 atm) and I know when she gets A6, she’s supposed to be insane buffing for DPS.

Next, what the heck do I do with Zelus 😅 I have no idea what’s going on with his build, and it says that it’s an ally buff too, but I can’t see where?

Finally (which one of those (aside from Nyx) would you have me star up? I honestly have no idea what I’m doing, and the only reason I did Nyx was because she carries me through everything. (Calypso is the next one, but idk I feel like a tank would help?) I need input from someone smarter than me, who has more than 3 weeks experience.

TL:DR - What’s Shamir do? How does Ferssi work and should he replace? Who the heck is Zelus😭? And which Lego do I star up?