i'd suggest fb, fahrakin, rearguard, corpse collector, and occult brawler. kael could be used while you're working on building up a few of the others, but he's really not that great a cb champ. his use in cb has more to do with the fact that a lot of accounts have him levelled early on rather than any inherent strength of his. occult brawler is a better poisoner and corpse collector adds additional poison as well as a leech debuff on her a1, which will go miles toward keeping your team alive. 

two others you may want to consider are fayne and coffin smasher. fayne is a bear to keep alive, but brings practically every debuff you need for cb by herself. i'd suggest subbing her out for fb from the get-go, but that leaves you without an aura (other than rearguard, which is fairly limited in scope) and as mentioned, she is the epitome of a glass cannon. coffin smasher isn't amazing for cb, particularly since fahrakin already gives hp burn, but he does have atk down on his a1, which is arguably the most important debuff to have for cb. rearguard and fayne together could probably keep it up consistantly, but it might be difficult to maintain with rearguard alone. that said, coffin smasher is definitely one i would view as a stopgap until you have someone better to replace him.

thanks  for  this.    One  question  i  have  is,  if  i  use  Corpse  Collector,  do  i  need  champs  in  lifesteal  still?

No, and that's the main reason for leech debuff. It's hard to find 5 sets of lifestael gear early on that have good stats. It's even hard later on, I could not build a team with really good lifesteal gear, and I got Cleopterix as log-in reward allready. 😼