lol but dude.....who the heck wants a pair of Convicts in a 75g? That's like...the most boring tank ever lolI also think you will get a lot more grief from a JD,a jewel a convict and a firemouth in a 75 than a breeding pair of convicts with a few swordtails.
As soon as sexual maturity kicks in I reckon the firemouth would be first to suffer assuming the fish were all the same age to begin with.
Cichlids will always see other cichlids as much more of a threat than a few shoaling dithers.
ultimately the decision is your, we can only toss ideas out there - consider Stanzzzz the side of "Order" and Frank Castle the side of "Chaos".....Maybe black phantom or red eye tetras