My JD isn't aggressive at all, in fact she's quite mild mannered. She stands her ground from my Firemouth and Nic, who are much more aggressive. I wouldn't have one in a 55g long term though.
IME Firemouths and Convicts are pretty much the same - pitbull bullies. Ellioti would be a better choice.
Same for me, I have a 4 inch Jack Dempsey and he's a huge softy.
He just minds his own business and roams around the tank, never takes a shot at anybody, not aggressive at all,
but will hold his ground when confronted by another fish (example: my male convict).
I have a mated pair of convicts, a small 2 and 1/2 inch female, and a 3 and 1/2 inch male,
and of all the fish in my tank (blood parrot, severum, oscar, jack dempsey), my male convict is by far the most aggressive,
and him and my female have began breeding, and I'm sure they'll start doing it pretty regularly now, it might be an annoyance to me.
You may want to pick another choice concerning the convicts.
and the minimum tank size for one jack dempsey is 55 gallons, its preferably to have a larger tank, at least 75 if you want a pair of Jacks.
If you were to have 2 Jacks in a 55 gallon, even though its not recommended, they must be the ONLY fish in there, and you need good filtration, frequent water changes to make it work,.