wow...first off a 55 is absolute MIN for ONE tiger oscar. 2 O's need 100+. I know male umbees get 20+ inches but not sure about females, but I can bet they get more then 15 in. If you do it you will end of with 2 mauled tiger o's and a extremely crouded umbee....
Umbee are incompatible with just about anything!
O's would be destroyed, not a chance against a Umbee.
Nothing of smaller size stands a chance, even most equal or slightly larger fish will be dominated and thoroughly worked over.
Male Umbee, average aprox 18" in aquaria, larger in the wild, 180gal minimum, prefer 240gal tank for a solitary male.
Female Umbee, average aprox 12"> in aquaria, a little larger in the wild, 75gal minimum, prefer 100gal+
Breeding is likely to end in disaster if great care isn't taken.
Thanks for all the info. Ive done a little reading on the Umbee's but all they said were they are agressive, never exactly how agressive. Any way, yeah the tank size is small. Working getting a 150 for the time being. Ill have to rethink the Umbee now I guess. Id only want the single female, due to size, but I also dont want to lose any of my other fish. Oh well. They are such gorgeous fish.