Best option might be for them to buy a second ticket from FLL to somewhere up in the Ft Walton Beach area. You can do a R/T FLL-PNS-FLL for $294, leaving FLL early on the 25th and returning early on the 27th. It's a bit of extra flying, but cheaper than the change fees. Of course, it's also pretty risky on the 27th, since they'd need to make a connection back out. Not to mention PNS is a good 1h15 from Destin.