Niether. barbs are schooling fish and do best in proper school sizes (6+). And, it has been my expierience that schooling fish do best when there isn't any other species of schooling fish in the tank(IMO, it also looks better too), so, I would just keep adding to the tiger barb population.
I agree the other barbs most likely wont school with the tigers. You may see them follow eachother around but they wont acctualy school. In fact most schooling fish wont school unless they feel threatened.