I have kept jewels in groups before, recently four in the tank below which is a community tank. But that was one male and three females which was problematic as the male kept breeding then losing interest and swapping partner. The pair are now in a 4ft raising young and the two females still in the display tank.
i have bred and raised a group of jewels in a 3ft tank before but that again was parents raising young to a good size. And I have raised 30 to adult size in a 6x2.
None of which were Turkana which are meant to be less aggressive.
(parent guarding young in a 4ft tank)
I would suggest you either provide lots of hideouts, rockwork, structure to reduce aggression (which will mean pairs form and take up residence) or you have very little structure, plenty of plants, so nothing really to fall out over. Then if you want to breed, move a pair to a seperate tank.
The option I would probably go with is a lovely display tank, with a pair and let them breed and rear them in the tank. You will then have a group soon enough, and with them being siblings they seem to fall out less (might just be a poor observation on my part).
You can have other fish in there, and then you will get to see just how good they are at parenting. But just be wary that catching them in a planted tank will be trickier.