I'll put this in this thread, for general purposes - TRIP CANCELLATION INSURANCE!!!!
I am bit of a cruise addict, and spend a bit of time on a message board dedicated to cruising. Almost daily, there are threads about "I have to cancel my cruise for xyz reason. Will Royal Caribbean/Carnival/Disney give me my money back?"
For us military folks, if we have a signed leave pass, signed and stamped before the travel was booked, you can get your money back from the government (as mentioned, for military member and immediate family). We've done it, when my husband was recalled from leave (only had to cover a hotel in that case). Another time, we almost had to get the military to reimburse us for a cruise when my husband was deployed on very short notice, but Royal Caribbean was very generous and allowed us to cancel for a full refund.
Most Trip Cancellation Insurance policies will cover if a member of your party has to cancel for a valid reason (work is usually a valid reason). So while the military will reimburse if the recall you/cancel your leave, if your extended family has trip cancellation insurance, that could apply.
Also, a good idea for the military member and family. If someone gets too sick to travel, you'll all be out the money. If a storm means cancelled flights (it is still hurricane season) and they miss 2 days of your prepaid hotel/park passes, etc. The military will not help with those scenarios. Cancelled leave is not the only reason to need to get your money back.
Just warning for people reading the thread. I recognize the poster with the question may be out of luck on this one. If the extended family doesn't already have insurance, it's too late. The military is not responsible for everyone's travel plans. They have to take their own precautions.
But nevertheless - have the extended family members check their credit card policy. Some credit cards have cancellation insurance built in as a benefit. Also, if they booked through a travel agent, some travel agents slip it in without you realizing it. They get a commission on insurance so it's to their benefit to sell it to you.