3 Zebrasoma tangs in a tank that size is going to lead to problems. Not saying it can't be done, but it will be a challenge.
Partitioning the yellow is a good start. I would expect to leave them separated where they can see each other for at least a few days. I have a smaller tank (6ft 120g) and didn't mix Zebrasoma's but I did have 4 tangs at one point. To deal with the aggression I used an acclimation box (which your divider effectively is) and a plastic locker mirror. I used an algae clip to attach the mirror to the side of the tank for around a week. They focused their attention on the mirror instead of each other until they got used to each other.
Not sure if that will work in this case because I was dealing with 4 different tang types which is easier but you may want to give it a try.