how big are the rbps? if babies then it would be ok, at least for now. eventually you will want larger tanks as they grow but you can tell if the tank is getting too small for them or not.
When buying rbp (assuming juveniles) always buy more than you intend to keep. Its easier to raise a group together than to add later and baby rbp are notoriously cannibalistic so expect a loss or 2. They are shoaling fish so the more the merrier in general