Here's my first stab, but you're going to have a hell of a time getting even 3-key UNM with it. You're missing a lot of very important pieces for a 2-key UNM team.

Sepulcher Sentinel (ATK down, Block Debuffs) - needs to be on a 4:3 rotation, if she's last, use A2 on turn 2, otherwise use on turn 3

Fayne (poison, DEF down, weaken)

Ghrush the Mangler (Leech) - turn off his A2 and A3

[Someone] (DEF UP) - Need to find someone else in your roster with a 3-turn cooldown, 2 turn duration DEF up. Thenasil will work if you have no better options, but ideally, find a DEF-based champion, since that way they'll be able to contribute for damage as well.

Ninja - pure damage

Sepulcher does def up with the block 

Sepulcher Sentinel brings increase def on a 4 turn cooldown together with block debuffs on her A2. I think another champion with a 4 turn cooldown should be enough to keep the buff up all the time, if 2 turns are between the first activation, so I recommend Steelskull. He brings some poison with his A1. The debuff bar doesn't seem to be filled completely with this team, Steelskull would bring some extra damage.

Yeah - but she can't also block the stun if she does, and it's easier to have her be a stun blocker IMO. Also, @Skadi, I'm hoping that OP has someone else like Grizzled Jarl that can contribute damage, since if he has to resort to someone like Steelskull, it's going to be real hard bringing enough damage to even 3-key UNM.

For NM:

Sepulchre sentinel lead, Ghrush (Only A1 enable) Rhazin, Banshee Ninja. Last slot experiment with Apo, Fayne, Aothar, Drex. Should be 2key NM with the right stats.

Wich last slot? Sepulcher, Grush, Rhazin, Banshee, Ninja are allready 5 champs. Or do you really want to replace Ninja with Drex? 👎

Won't work, unless you're willing to let someone eat the stun. Which I guess you could do, by making Ninja the lead, but you'll lose a *ton* of damage if you do that.