You have Death Knight, Ninja, Arbitor AND Ronda but not Mithrala? How on Earth did you do that? Do you not belong to a clan or doing Hydra? I also don't see Yakarl but then you're asking about Clan Boss so I'm really confused by your roster.

Well... Ninja is really strong for CB and Geomancer is too. You can also use Arbitor to boost your turn meter along with her heals, increase attack and rezzing. Of course, the right gear is very important for all of them as well. Poisons do a fairly good job at damaging the CB so the Xenomorph is a good 3rd DPSer as well. Then you just need a debuffer that can do decrease Atk and possibly Hex too.

I use Mithrala for my 1 key UNM team. Not only does she have hex, but she's also putting out shields, cleaning debuffs and giving really good buffs with strengthen, increase Atk and Def. Plus, her main attack it putting on poisons for decent DPS. I don't know who could replace her for your team.

With those 5 champs, you should not have an issue doing 2 keys then. Just remember to keep your speed up with yoru gear too. Slow champs do less healing and less dps and have a harder time stacking on the debuffs.

If you're looking for a 2-key team, I wouldn't overthink this too much. Just go with a standard 1:1 rotation, IE, speeds between 170 and 189. You'll want:

1) Brogni (block debuffs, atk up) - needs to be slowest so that his block debuffs prevents stun. You'll want to delay the A3 by one turn so that it goes off before CB's debuff AoE.

2) Brago (def up, atk down) - second slowest, Brogni will lose DEF up for the second attack unfortunately, so make sure he has enough DEF on his own (IE, at least 3000, ideally closer to 4200)

3) Geomancer OR Ninja - Ninja will have a higher damage output, but Geomancer will help keep your team alive more.

4) Your favorite Leech debuff champ. Vogoth works, though his contribution to damage is pitiful, so ideally find someone better.

5) Anyone can fill this spot. Options include Aniri, who makes it so you don't need to worry as much about Brogni's DEF, since the extender ensures all your buffs remain active always. Venomage is also a strong choice, since her passive reduces boss damage. You could even go with Ronda, though I have a feeling your gear isn't good enough for face damage to be worth a spot.

NOTE - I see you have Seeker, so keep an eye open for enablers for unkillable/blockdamage teams!