I have seen Oscar and BP in 75's work. With a 90 it would be better. It could work as far as needs go, as far as personalities that's a different story. You would be able to keep only 1 of each. You would need to add Silver Dollars, Giant Danios or other larger fast fish for dithers if needed. Giant Danios would be a better choice based on tanks size and SD would be better choice if kept in groups of 6, requiring a much larger tank.