I would add more Yellow Labs. They look great in numbers. Yellow Labs are probably one of the most mild African Cichlids. As such, though, they may be prone to being picked on. I did a lot of research to figure out what would be compatible with my six Yellow Labs and it was not easy. I wouldn't get anything that you find with a temperment more than Aggressive or better yet Mildly Aggressive. I have found that some Malawi Peacock species are very compatible with Labs. I have two Ruby Red Peacocks and a Midnight Peacock that coexist nicely with the Labs. As well, I have several Yellow Tail Acei that are no problem at all. I have a Ps.Johannii (Aggresive) that beats up on the others, and is constantly about 2 nips from being banished from the tank. Do yourself a favor and research well before deciding.
By the way I looked up the Auratus. If you have Melanochromis Auratus or Melanochromis Mossambiquensis, they have a Highly Aggressive temporment. If you have a Melanochromis Parallelus, then it has a Mildly Aggressive temporment. You may want to look the up to see which one you have. If it is one of the first two, it may become too much for the Lab(s) to handle once it reaches maturity.