Agree with the others about the tank size issue. I currently have a TIger O, Lutino O, and a red O in my 125 but I am also doing 1 50% water change a week, and my tank filters around 13X my tank volume an hour.
Temp the oscars can live with. Consistent raising and care is what matters the most. Do some more research, and feel free to ask question ahead of time before buying the messy beasts.