Depends on the species. Agree that a trio of lyretails could work in a 90, though they’re certainly not on the less aggressive end of the pseudoanthias spectrum. They’re part of the Franzia subgenus which boasts some of the most pugnacious species. They are, however, generally easy to feed and less exacting in their requirements. They do need frequent feeding otherwise you may well find your trio as just the single dominant fish. My personal favorites are bimacs, but they’re probably too big for a 90 .... plus they get pricey. Dispar/ignatus would be a good choice. They stay smaller, aren’t quite so homicidal, and you could probably keep 5-7 in a 90.