Duanes' information is correct. However if you buy fish which have been bred in captivity for a few generations (all the species you listed can be commonly found at big box stores) they are pretty adaptable to pH and gH, usually to local tap water. I wouldn't chase parameters and try to alter it for these fish.
The first combination you list is better, the Midas in the second would be a wild card.
Oscars and jack Dempseys have been a classic pairing for years, and can certainly work together in a tank. I have combined them myself and seen many do it successfully. If your Oscars are an actual pair and start to breed, that would be an issue, and they would probably bully the other fish into a corner. The green terror could also be an issue, but I think you have a decent shot of making it work in a properly sized tank. I would go for minimum 180 gallon to try this.
The first combination you list is better, the Midas in the second would be a wild card.
Oscars and jack Dempseys have been a classic pairing for years, and can certainly work together in a tank. I have combined them myself and seen many do it successfully. If your Oscars are an actual pair and start to breed, that would be an issue, and they would probably bully the other fish into a corner. The green terror could also be an issue, but I think you have a decent shot of making it work in a properly sized tank. I would go for minimum 180 gallon to try this.
