I'll try to help you out as much as I can. Starting with the assortment of fish.
1 Oscar - 4-5"
large (14") but not agggressive
1 Red Devil - 4'5"
large (12"), extremely aggressive, cannot be kept with any of these other fish in less than a 200g tank (and thats risky)
2 GT's M+F - 3-3.5"
medium sized (8-10"), moderately aggressive
3 JD's - 3-3.5"
same as Green Terror
2 Brazilliaras ? - 3"
probably Geophagus brasiliensis, large but not to agressive
2 red belly pacu - 4-5"
Extremely large, but not aggressive, you need to take this fish back imediately, will grow to over 24"
1 Firemouth - 3"
medium small (5-6"), not aggresive
2 silver dollars - 3" targets
small (4") good tankmate for most cichlids
2 Plecos - 3.5"
large (18"), good tankmate for most cichlids
4 Corys - 1.5" they hide alot
Dinner, or a death trap (if their spines get caught in the throat of a larger fish, these must go back if any of the others are kept
1 Spotted Gar - 6"
Could be a true gar, like the pic that was posted, or a Characin species. If its a true gar I would expect it to reach atleast 24'
I'm going to suggest that you keep the
1 Oscar
2 Green Terrors (because you already have a pair)
1 Jack Dempsey
1 Brasiliensis
1 Firemouth
1 Pleco
2 Silver dollars
But only if you can get a 180 gallon. If you go larger (250g) you might be able to keep the gar depending on species.
When the GT's spawn they will lay the eggs on a flat rock or driftwood usually. This will be very obvious. There may be over 500 eggs, probably less because they are still young. The eggs will hatch in a few days, and a few days later will be able to swim. They do not bury the eggs, but may move the fry to a safer place. If you want to save the fry you should divide your tank with an egg-crate divider. The Gt's, may become extremely aggressive during breeding.
HTH, I wrote it extremely quick, I have to go,