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.