ok here it goes........
i had a yellow tang in my 80 gallon I added a blonde Naso and a sailfin tang like 3 months later. The yellow tang had been eating fine and everything when i added the other 2 the yellow went nuts and beat up on both of them. I got the yellow out of the tank and the blonde naso and sailfin were GREAT TOGETHER!!!! Well i came to realize my blonde Naso was not eating from the algae clip.(i found out to be a common problems with some Nasos) I did everything i could to get the naso to eat i had 3 clips of veggies all over the tank but some other algae in the back corner of my tank he never took to any of it so he did die im guessing of starvation. So i was left with my sailfin still doing great and eating like champ. I then added a regal and they are like best friends they are always all over each other and they both tear up any type of food that goes in that tank. They will eat ANYTHING!!!!!
so my advice to you is this.
Add The Regal and the blonde naso at the same time so that neither of them has a chance to establish any dominance alone in the tank. Once these two are in your tank eating and loving life for a couple months you could take a chance at adding the yellow. I deff. would NOT add the yellow first simply because i have heard so many stories of the yellow tang being so aggresive if it is allowed to establish dominance as the only tang in the tank. plus i think the regal and the naso are pretty non aggresive where as the yellow is classified as aggresive.
This is all just my 2 cents and my opinon but i figured i would tell you my story if it will save you some of the troubles i went through.
also if you ever have any problems getting them to eat.....soak some of the nori or veggies sheets in garlic before you put them in the tank