Bad El is an absolute must, he's amazing everywhere including in CB. Elhain and to a lesser extent Skullcrown are poor fits for CB and should be taken out as soon as you have better options - not much point bringing AOE nuking champs against a single target. Although SC does have weaken and a nice passive, so you'll want to keep using her for longer. 

Ideally, you would want 100 percent uptime for both decrease attack and decrease defense on the boss. Weaken is nice to have as well, but less essential. And then you try to get as many poisons as possible. Between FB and BEK, you should be OK for poisons, but you're going to need better solutions for the attack/defense down debuffs. Tayrel would be an upgrade over Warmaiden for sure, but I don't think Spider is - sure, the chance of weaken is nice, but the cooldown is too long. 

I'm also not sure why you have a frost set on Doompriest, that doesn't seem to make much sense? Otherwise, she's decent for CB, although Mausoleum Mage would be an upgrade. 

So in the short term, I'd definitely replace Warmaiden with Tayrel and Elhain with BEK. Afterwards you could consider to potentially replace Skullcrown and Doompriest at some point.

The frost Doompriest is me being cheap ass, and making her multi purpose Arena, CB etc. I'll change the setup as soon as I have the required resources.

Tayrel- BeK- Septimus- Apothecary- Frozen Banshee should do for now. Once you pull a counterattack champion, you can replace Apothecary, and maybe replace Frozen Banshee with a properly speed tuned Roshcard.