I have one male and 3 female gymno. labiatus 'rio olimar' in a 40 long. Same foot print as a 55 but not as tall. I don't think I would be comfortable putting 2 more in the mix. It would probably be awful crowded. I have 8 coryadoras paleatus in with them. They can take the cool down period...
To agree with everyone else, it doesn't look good for the fish. As platytudes said, Thiamine deficiency has a lot to do with it and feeding goldfish has been proven to lead to that. Something in the goldfish prevents cichlids from absorbing thiamine and over time it will lead to this. Good...
Personally I would get the python over the aqueon. the python tubing is much more flexible and easier to work with. I have both and I much prefer the python.
If you think you have trouble keeping it clean now, wait about 6 months. Way too many big fish in that tank. I am sure it is fine now, but those fish will grow fast.