Too many?

[talldutchie]

I suggest you start by observing carefully.

I see it this way:
you got a few potential issues
1. interaction with other species. In a 20 gallon that's likely to lead to problems with anything that's not a strict bottom dweller.
2. Swimming space. Not much you can do there except upgrade.
3. interaction between the tiger barbs. Here's where uncertainty sets in. I've seen this species build up a hierarchical structure that reminds me of birds. There's one or two boss fish, quite a few in the middle and one or two that are at the bottom of the school. If those bottom fish do not get harassed so much that they suffer physical damage and if they still get a chance to eat you do have a shot at pulling this off.
On the other hand, I've also seen them where 2 or even 3 distinct groups formed and there was constant bickering. That stresses everyone out

Even if you do manage to get a school that works well you sitll have the issue of a relatively low amount of swimming space that I feel you need to address sooner or later.

But, this is just my $0.02.

[Goes to 11!]

+ 1 to the above.

Well... what do y'all suggest be done? I don't know if I can take them back to the store.

Finding out is your first step.

[Compass]

Well, first off, I've decided through the course of this thread to put nothing else into this tank.
Right now all the fish seem to get along. There is some chasing but I figure that is to be expected. Nothing non-stop and no one fish is singled out. Also they all get to eat, none of the smaller ones are pushed out.
With that being said I am going to house them in this tank for the time being. I know a larger tank is ideal and I do want to get one, but I don't know when that will be. I keep a very close eye on them. Sometimes just sitting and watching them for an hour or so. So far they are fairing in this tank.