You can't make a community tank in a 2 or 3 gallon, period. Think 10 gallons at least if you want any sort of variety. You can have a small community in a 5 gallon, but we're talking 5 small critters tops, and you have to be careful about what you choose.
Unless you're planning on buying a 20-30 gallon in the near future, rehome the goldfish or return them to the pet shop. They
will die in that tank if you don't, there is no question about it. In a 2 gallon you can have a betta and a couple of ghost shrimp, a snail or two (depending on the type of snail,) or an African dwarf frog... NOT the clawed kind.
This site can teach you how to tell the difference if you don't know already. The clawed ones are what your brother has, and as soritan said, they grow as big as your fist and eat anything that will fit in their mouths, including fish and other frogs. You've got basically the same options for the 3 gallon, but you could chance 2 ADFs instead of just one.
Everybody makes mistakes, I know I did when I first started fishkeeping, but in the future it's very important that you research your fish before you buy them. If you see something you like at the LFS, wait and look it up online, then go back and buy it if and only if you can properly house it. Don't trust what an LFS employee says unless you are absolutely sure they know what they're talking about... most of the time they don't, it seems
