First, that 2.5 gallon is totally inappropriate for even one single goldfish. If you want two goldfish, you need a 20 gallon tank. For three, 30 gallon -- they grow to 8 inches or bigger. if you KNOW FOR SURE you will upgrade in a year, you can probably start with three smalls in a 20 gallon. Never use a 10 gallon for golides. You can get any other goldfish that has eyesight issues, so they all can eat. Like a black moore, or even an oranda. Not a regular goldfish, since their bubble eyes are very delicate. No other kind of fish but goldfish. DO NOT get a pleco or bottom dweller, they will kill these fish. Good luck! PS, goldfish DO do better in groups, but only if you have the space. They will be unhappy by themselves, unless your tank is uber small.