Maybe someone can confirm, but I believe the smallest UPH available is a one night/two day. It would be good from check-in until midnight of the next day. The advance purchase price for this is $119, or $129 at the front desk when you get there, for one adult. As far as I know, I don't believe they can split this up and have it be valid, for, say the check-in day but not valid the next morning- the UPH are sold by the number of nights, not the number of days. So, I guess it depends on what your relatives are going to do, whether this is the best choice. If they're only going to spend one day in the parks, and only hop once, from, say, Magic Kingdom to Epcot, then two one day/one park tickets might be a little cheaper. But just about any other option- more parks, the second day hopping, etc, the UPH is probably better. Also the convenience of just putting the ticket on the room key with the UPH might make that the nicest choice too.