That may work.All fish are different,so you never know what will work and what won't. I am assuming all the fish are small right now,so because you have plenty to choose from,wait and see which ones get along,and you may see which ones are less aggressive toward the other fish too.Just be prepared for one of the GT's,or any of them for that matter,to live up to the aggressive nature that these larger cichlids have.
But there are plenty of people who keep FM in community tanks with out any problems.I also know people have Cons that do fine with other larger cichlids.I have a GT that won't put up with other fish,but know people who keep them and say theirs are total wimps with other fish.The biggest concern you should have is that a 75 gallon is a descent sized tank,until you stock it with some 6" to 12" fish that may have attitudes.Then watch out.
So who knows.Wait and see what happens with the fish you have,and which ones get along.If you plan on keeping 4,overfilter.These are all fairly large fish,(especially the BB) and produce a lot of waste. Keep up with the water changes too.