I think you can keep pair of young (small) convicts in a 10 gal. Just do lots of water changes.
Sell the pair when the fry are 3-4 weeks old and raise some of the fry and sell or give away others, when they start pairing give away all but one pair and start again.
Fish dont have to be in their orginal tank all their lives, you can take them to the Lfs or give to a friend with bigger tank, but if you like them, you just buy a bigger tank !
Note ! I think keeping 2 adult convicts in a 10 gal. should not be done.
...but small pair 1-3" ? I always keep cons as feeders, have a adult pair in a 29 gal. and I also keep a young pair in a a 15 gal. next to my Oscar tank, I do water changes once a week and they seem happy, when they run out of space (usually when the male starts attacking the female when they are raising fry) I give them away and start with a smaller pair.
One Female con would be fine.. but like stated when you get into pairs Cons are better off in with 3 feet of water territory Rams are an excellent suggestion