There is absolutely no reason you should be failing on doom tower level 4 normal with your team. What's your gear levels look like? Are they running at least level 12 gear? The champs are more than enough to get through there.

I  thought  so  as  well.    However  i  am  getting  decimated  at  round  2.    Cant  kill  the  bomb  throwers  fast  enough  and  then  they  desimate  me  with  2  straight  quick  bombs.    

all  gear  is  12+ .    Kael  has  22 k  health  and  gets  wiped  out  by  the  bombs..

sub Coldheart out for some crowd controller, Stun/ provoke, or a chunky boy with shield set, or someone who does better dps on waves

I dont think coldheart works that well on waves, so no reason to have her in there

addendum: you could also try to run someone with resist aura and see if they can resist the bombs? and equip your vulnerables with resist banners

Do you have anyone who can do AOE cleanse? Reliquary Tender or even Spirithost? That's usually the best solution with bombs - or put a block debuffs at the right moment, or indeed high enough resistance but that may not be necessary. 

doh yeah, forgot cleansing. probably the easiest solution if you got one

Honestly though - Sicia should be able to solo doom tower until around floor 40. Your team should not be losing unless you have something seriously wrong with it. Could you post screenshots of your gear/stats?