The Flowerhorn in the 55g might co-exist with a syondontis catfish or two, and perhaps a pleco (give them plenty of hiding places, though). Other than that, no new tankmates. The tank is too small, especially for another cichlid.
Your 125g is also full, perhaps even overstocked if the Flowerhorn develops agression issues vs. the other cichlids in the tank. Cichlids are territorial fish, and large cichlids in nature will stake out territories that are 4 feet in diameter or more. Thus most tanks in our hobby are not large enough to contain multiple competing species. With Blood Parrots, severums, and Flowerhorns, your current tanks are at capacity. If you want additional activity in the 125g, you might consider adding a school of large rainbows or silver dollars. If your cichlids are large, you definitely need to buy larger schooling fish or they will get eaten before they have a chance to establish themselves.