Hi, if the convicts breed then they will push all the other fish into the other end of the tank and attack them. they can be very nasty for there relatively small size but the jd and fire mouth should be able to withstand them.
a JD would eventually kill them but the convicts would terrorize the whole tank until then..or even after..but i never really knew anyone who keeps a firemouth single i thought there more shoaling..but id switch the convicts maybe even a jd for a green terror..
gt will get too big for a 55 they will eventually outgrow it... i would go with convicts and firemouths ther are also salvinis they are colorfull and xcan live in a 55 for life