Just curious how large is your tank?
Green Terror's and Jack Dempsey
's get very very large.
I would tend to stay away from the rosy barbs and go with Tiger Barbs. Tiger's in my experience are a more aggressive fish and could hold their own better than the rosy's.
If you get a pair of Convicts, or any cichlid like them you are going to have to monitor your tank close as they will beat the crap out of everything else in your tank. They have been known to hold their own against fish three times their size.
Severums get large (8"), but are relitively peaceful compared to a Jack or a Terror, but still need their space. Firemouth
's stay around 5" and would be a similar size to the convicts and have enough toughness to hold their own against convicts, but like I said, a breeding pair of convicts is dangerous in any tank.
I would go with the Firemouth
and Tiger Barbs depending on tank size you might want to try to find a mate for the Firemouth
Convicts are a beautiful fish.
Hope this helps.