Before I would completely SCRAP the family vacation, I would look at other options even if that included having to drive. I dont know what airfares are in your area, but I started flying on Frontier and have been able to make it work. Like many before me have suggested, I would look at VARIOUS options. And who says its a rule to have to book a Round-trip ticket. I haven't booked round trip tickets in YEARS!!! For the last 6 or 7 years, I have been booking ONE-WAY flights.
I fly out of Philadelphia. I always book my returning flight FIRST because we always leave Orlando on a Saturday. Saturdays can be more expensive so I book the Saturday flight back home first as soon as the price drops to something reasonable. Then I start looking for my flights down to Orlando out of Philadelphia. I use airwatchdog app, frontier airlines, and southwest apps to alert me of the lowest fare from PHL to MCO. One year I went to Orlando via United Airlines and returned on Southwest airlines. Who says you have to use the same airline?? There are no rules to that!!! I think you are having a difficult time because you are trying to book perfect matching round trip flights. Book one-way flights and open up more options!!! Cancelling a family vacation should be your last resort. If flights don't work, then drive and make that part of the vacation too !!! Good luck in whatever you decide !!!