Your bottom fish are Silver Dollars, Metynnis argenteus and they are related to Piranhas and Pacu. Your pale fish next to the pleco is a cichlid too. All your rainbow types look like various Lake Malawi cichlid species.
When I was breeding fish, I found that excluding the parents is the best way to save the fry. Fry are delicate and don't like being moved to tanks where the water conditions are different so you either leave them where they were born and catch the parents and put them elsewhere or make some kind of netting partition for the tank
Yeah its tricky they seem to give birth while I'm at work then I notice they are no longer pregnant and there are no fry in the tank either. Crazy canniballistic guppies. For some reason it only seems to happen in my smaller tank, the bigger tank the fry survive well.
Now that silver dollar name rings a bell, the cichlids are quite diverse in their shapes and coloring. My favorites are the red devils.
More space does seem to reduce the cannibalistic instincts in fish
I guess I also have dragon guppies in the other tank, I wonder if they are more aggressive.