Nope, that won't work. You can't keep all of those fish in a 55 gallon. The Geophagus brasiliensis can reach a length of 11" and isn't a good choice for a tank if this size.
A pair of Keyhole cichlids would be fine in a 55 gallon. They are pretty peaceful cichlids and be a bit shy at times. Instead of the Tiger barbs a small school of Lemon or Black Phantom tetras would go well with them and help them to overcome their shyness. The addition of the RTBS should be okay but they can become more aggressive as they age. This would still leave plenty of room for a Bristlenose plec or a few cories.
The Rainbow cichlids, Herotilapia multispinosa, get slightly larger than the keyholes and are a little more aggressive but they are peaceful unless they are spawning. If you don't want to them to breed you could go with one Rainbow cichlid, the RTBS and the Silver dollars. The Rainbow cichlid as well as the RTBS need a good amount of veggie matter in their diets. The Silver Dollar is a Herbivorous fish.
Bryan
