IMO getting them around the same size would be better and removing the trouble makers would give you a better chance at getting a match. From my experience with dwarf cichlids if one is older and has established a tank of its own any other member of the same species is fair game for harassment and the little guy almost always suffers. This may be different with rams, I can not say as I haven't owned any personally. This as just based on my experience with cichlids in general.
The trick with adding juveniles to an established tank with adult Rams is density. I have had about 20 juveniles growing out with an adult male in a 30 gallon and all was fine. When they first hit the tank the male chased them for a couple hours, but settled down after this. I would do at least 5-6 juveniles with the adult ram.
Rams are generally most aggressive to other fish when they are breeding. I have also had a dark Ram male kill a female ram after spawning.