What size tank do you have? FM's get rather large compared to some of the other fish you have there so taking both back might be your only option anyways. 2 FM's should be kept in a 55g minimum. Your BGK get's even bigger and needs a tank twice that size to accomodate it.
Hoping you do have a tank large enough- This usually happens when you have 2 male cichlids together in a tank. If it were me, I would take one of the males back. You could get a divider, bigger tank or exchange the male with a female if you have a tank large enough for 2 FM's.