the regular barbs and the green barbs should have no problem schooling together. you would definitely want to remove the barbs that are already in the tank, rearrange things a bit, and then add everyone together.
however, IMO a 10 gallon is too small for 6 tiger barbs even if they are still juveniles right now. you will probably see a lot of aggression from them (more than is usual) in that small of a space. they will already been pretty much full grown in a couple years, so if you were to get the barbs now i wouldnt wait any longer than three or four months to upgrade to at least a 20 gallon, 29 would be preferable.
good luck
