In a 20 gallon, 2 males will probably not co-exist forever. If they are small, you may have a while. Switch for a female would be better, or even better, keep your favorite male and try some quick dither fish like swordtails.
The last guy's advice was not good in my opinion. We know the sizes convict cichlids can grow to as a species, and their average temperament. This will be true of convict cichlids in my tank, your tank, his tank. You don't always have to "learn only from your own experience" when there is a wealth of information available today from people who actually know what they are talking about. Will save you from experimenting too much unnecessarily. I'm sure the fish will appreciate not having to be guinea pigs.
That said, convicts in a 20 is not the worst situation. I've bred them in smaller before. But to me, a 20 will eventually be too small for a pair, but should last you until the male is about 4" TL. To grow beyond that and reach full potential he may need a larger tank.