I am moving up to a 75 gallon here shortly. All male tank is the most docile.
My tank dictator is a blue pseudotrophus elongatus, In an open tank he is a real jerk.
In a tank with lots of corners. That he can't see around. His 2.5 second attention span keeps him pretty docile. Except around his claimed cave.
Yellow labs are easy to get along.
My female firefish only boss each other around. I had a male once but he got evicted. He was a pain in the ass. My new male is smaller than the females, So far he is peaceful.
One problem with cichlids is identify males, in a group of juveniles, most of mine have been together since they were just 3/4" fry. About 2" now.