Those are a couple of tangs that can potentially be pretty mean, as can most. How big are they? Size of them vs the sharks is certainly relevant. Many have accounted of purple tangs with a mean streak. Cat sharks require pretty placid tank mates as they are pretty defenseless against anything that isn't prey. I would personally give it a shot as those are two awesome fish and it could work, the chances are in favor based on tank size (the 300). Adding the sharks to the 90 will be another thing altogether initial aggression from the tangs could be unmerciful. What type of wrasse and goby do you have? I cant think of a goby that would not be prey for a 2' cat shark, they are sitting ducks for predation. I would think the sharks would eventually hunt down the chromis and wrasse (dependent on the wrasse, bigger ones who wouldnt be prey sized are generally pretty mean and would likely pick on the sharks). The zebra eels are very large and placid, it will make an excellent tankmate.
Just my opinion, I am by no means an expert.
