I'm not trying to be harsh, but some of these stores are the same that will tell you a betta or goldfish are fine in bowls. They want to sell you things.
I actually completely forgot something when I last commented. You do want more of them as the zebra danios and torpedo barbs are shoaling fish, meaning they should be kept in groups of 6+ of their own kind.
They are likely happy for now, but it's best to plan for the eventual size of the fish. That rule is rubbish IMO as it doesn't account for everything, such as activity levels.
Or bioload..such as a 4" pleco is going to put off a lot more bioload than a 4" tetra.
So even though the zebra danios are small, they are very active. This is why people recommend a 4ft tank for them.
Zebra danios get up to 5.5cm, torpedo barbs 15cm, angelfish 15cm, parrot 25cm.
Again, I'm not trying to be harsh or rude at all
I just wanted to let you know this information that way your fish can be happy.