in that tank, one will live about 6 more months (then be Killed) and one will live 1 more year. Then it dies unless you have one of the few stunted Oscars Bred in RI. I can tell you if it is one of them since i own one.
Normal oscars, Given adequate food, water conditions, housing, heating, and attention (They are as smart as Dogs and need human interaction)
Tiger- 10-20 yrs
Normal Coloration- 12-25 yrs
Reds- 10-20 yrs
Albinos- 3-5 yrs less than whatever color variant they are
You are also located in RI, so email me and if need be i can show you the proper housing for an oscar. these fish WILL DIE in that 30G!
Hell, if ya wanna see some Cool tanks, I offer an open invite.
Good luck, BUY A BIGGER TANK!