If your roundtrip was $184, did you try pricing a one way ticket for your return flight? It might actually come out cheaper than paying the $200 change fee. Because really after deducting the $200 penalty from the value of your ticket, you're left with no credit to be used toward a new ticket. In this case, it's more cost effective to forget about the tickets you already have and book the one way return flight. But if all 6 of you are on the same reservation, make sure you notify Delta which 3 passengers are not flying so it doesn't affect those who are.