Aox is just "okay" for CB. He brings some value from poisons and increasing debuff durations, but overall, he's not a huge contributor. I'd probably drop him.
Valk is of course a beast, and has to stay. Frozen Banshee as well.
For the other three spots - I'd go with Ghrush for Leech, Sepulcher for block debuffs and DEF up, and Sandlashed debuff extend and ally protect. You'll need Sepulcher to be on a 4:3 rotation, as her A2 is on a 4 turn CD.
For Ghrush, disable his A2 and A3 - you 100% need to keep leech up constantly, so you can't afford to lose a turn using his other abilities. For FB, of course, disable A2.
You want Sepulcher Sentinel going last, and using her A2 on turn 1. Sandlashed then uses her A2 on turn 2, to extend the DEF up and block debuffs to 3 turns, which'll allow you to have the stun be blocked. The turn order for the other four champs doesn't matter too much.
With the right gear, this should be easily capable of 1-keying NM, and shouldn't have any trouble getting to at least 3 key UNM, probably two key.
Ultimately, you'll want to replace Ghrush with Corpse Collector, who just brings more value overall because of her A3 placing three poisons. The rest of the team, though, is pretty much set in stone.