well, its better u let one RTG fix around with ur other fishes....its more u put more tankmates..but that depends on ur size of ur aquarium, don't over load them...u might give the RTG a heartatack..hehe...and then slowly observe..the RTG..a week..see how it settle downs with its tank mates..
later u put the YT...and see how it goes..it might juz work nicely with both of them..hehe..all the best mate..