What should you do? Not accepting these fish in the first place leaps to mind, if you have no place to keep them. By definition, a "rescue" needs to improve the living conditions of the rescuee...
But, if you already have them...and can't quickly find them a better home...why don't you set up a smaller tank right next to the already overcrowded main cichlid display tank? If you place it so that the tops of the two tanks are on the same level, you can set up a siphon from the main tank into the small one, and then use either another siphon with an air lift or a small circulating pump, wavemaker or powerhead to return water back into the main tank. The small tank will "piggyback" off the main tank's filter and heater, and won't really need much or any maintenance itself aside from vacuuming the bottom periodically. It's not a true quarantine tank since the water is shared, but at least it separates the little guys from the big guys.
They'll grow fast, and might or might not someday be able to go into the main tank depending upon the size and attitude of those cichlids in there. But seriously, you should be looking for another home for these fish.