unfortunately not, 90 gallons isn't really big enough either. If you get two Severums and they are male and female, the chances are they'll pair off and start breeding. Even though I wouldn't class Severums as aggressive, they can be quite defensive when they have eggs, 90 gallons wouldn't really give the fish enough room to avoid each other, the Severums will probably get extremely stressed with the Oscar there. You will probably be okay with around 130 gallons and very good filtration.
You got a little bit careful with cichlids, mixing them can lead to aggression problems. If you want a couple of cichlids to go with your Oscar, see if you can find some Jade eyed cichlids. These lovely little nonaggressive cichlids come from Central America and are quite delightful.they don't get much bigger than 6 inches.
