Just wait out the QT for the fish you have now and get some additional fish for that QT tank after ones just purchased go into the new tank.
Probably do daily or every other day pwc
on the QT, to keep the water perfect and five these new guys the best chance possible in the QT transition period. I (accidentally) have killed fish in the QT because of missing a water change or not having enough BB to handle the new fish load.
I would give the time of a couple weeks to 3 before adding new fish to round out the groups. When these guys are good, buy the newest ones for QT and then 2-3 weeks the BB should be catching up for the next ones to go in.
Just watch the main tank parameters too, pwc
more than usual during the new fish adding stages.
Feed enough to eat but lightly (or divide the portions for AM/PM too, young fish like food more often) so there aren't leftovers and it will go pretty well I think!