It is the queen angel you have to worry about. It definitely will not take kindly to a new addition. Especially not to a good size tang, which it will see as competition. You definitely don't have a large enough tank to house them individually for seeing as how they are both very active swimmers and territorial.. The established queen will pick the new addition to death, you can bet on it. Not a good idea.....And as for your statement about everyone needing "500 gallon tanks", sorry but it is just not applicable. Certain fish need certain requirements met. Some special feeding, some special tank size, etc. Both of the fish you named don't belong, and won't do well in a 90g. Just the facts, sorry.