Way of the Wicked Advice, in Book Two

[Gruzzle]

As titled, running book two of Way of the Wicked PF1e. Hexor and Vexor are tanking everything, and I feel like the first half of the weeks of rituals have been no challenge. The Banner Verdant is coming up in a coulpe weeks, and I'm thinking of having Ezra the Thrice-damned make a move early? Any ideas how I can make Ezra a challenge, or any further encounters for that matter? If Verdant sorcerer got a lucky scroll of banishment off would it permanently remove a ceusto-demon from the plane, or would they re-appear because of the necklaces? I haven't been able to google-fu my way to an answer on that last one. Thanks in advance!

[redking]

Need more context to give answers. For example, "Hexor and Vexor are tanking everything". How did they manage that?

[Gruzzle]

In the AP (spoilers?) there are two greater ceustodemons (dimension door at will, DR 10/good or silver, AC24 Large outsiders with over 80hp each.) who the party can fairly easily bind to their control through Iron amulets which contain the true names of the pair, and if killed they simply reform next to the amulets a month later. The party has casters who use infernal healing and the dungeon they're in further improves their survivability. Furthmore, nothing that I've read so far indicates the party can't drag these two greater ceustodemons along with them for the next 5 APs. They have fly and dispel magic 3/day and hold monster, DC 19, 1/day. coupled with a +13 to hit and 3 natural attacks in a full round for a potential 4d6+18, they can nearly duo most early threats without the party playing ranged support. But with them? Whoooo man, it's rough. I've come up with ideas on how I might trim down the volume of followers with the Banner Verdant, but I'm also in a bit of a pickle because one party member has taken Leadership (AP encourages this) and his cohort is a gnome built for magic item creation. She would be easy pickings but I'd feel bad killing her off, the party quite likes her and the player made a big effort to write up back story and history for the cohort