Whereas 75 gallons isn't really big enough for two Oscars, it's certainly a lot better than 2 1/2 gallons. I think with regular tank maintenance and good filtration, you might just cope but that doesn't mean I am recommending 75 gallons for two Oscars. As for the other fish, don't even think about keeping them. Pacu can reach 3 feet, these are really only suitable for people who have suitable tanks. As for the bottom feeder, depends what sort it is. However, I would just keep the two Oscars if you do yet the 75 gallon.