Generally i would say (in order of importance) you want for a clan boss team
Someone with attack down on their A1 (essential)
Someone with defence down and ideally weaken (essential)
A poisoner (important)
Someone who can ally attack or counter attack (really nice to have)
If not using a speed tuned unkillable team a turn meter /speed champ (nice)
A cleanser (stun remover) is also nice but i dont think people consider it important
- for healing, if you have warmaster/giantslayer masteries then you will heal from the procs if in lifesteal gear
So
Sepulcher sentinel for attack down- top tier champ.
Rhazin for decrease defence and weaken (he is a solid champ)
Vizier to extend poisons and another attack down as backup
Frozen banshee to apply poisons and sensitivity
And personally i would go with fahrakin for ally attack over grush, providing everyone is in lifesteal... the reason is not only will you get extra damage and more poison procs from frozen banshees a1 , but you will get extra chances to apply the a1 attack down. I personally think that without a counter attack that fahrakin is the next best thing
But try switching fahrakin for grush perhaps see which works best