Your green tiger barbs will school with the regular tiger barbs, no problem. I'm wondering what size tank you have. As a general rule, Tiger Barbs and Black Phantom's will go well together in tanks larger than 29 gallons. Keeping Tiger Barbs in a tank any smaller than this can be extremely difficult, because they need a ton of swimming space to curb their nippiness.
You say that you "plan to have" a school of 7 Tiger Barbs. I am assuming that you do not have them yet. If will help if you make the Tiber Barbs the last addition to your tank.