We did a scavenger hunt with Gift of a Lifetime on our last visit; Mom and Dad, all three kids, their spouses and 7 grandchildren. She was great to work with and answered all emails promptly. We set up out preferred place and time, and decided on girls versus boys, so all spouses and families were split. Our hunt was literally all over EPCOT, and set up so we had to do certain things at certain places and times.
I will say that although it was pricey it was worth every penny! She has helpers throughout the park, and we never knew when we were being watched or who would hand us the next clue. It culminated with a trophy and certificate for bragging rights to the winner, which I had provided her.
We have visited Disney countless times as a group of 15, and pretty much covered all of the extra type adventures you can do- SPA, surfing, SEGWAY, horseback riding, golf, pirate cruise, fishing, fireworks and Grand Adventures. So being able to arrange this and do something unique that the whole family could participate in and be surpassed by was priceless! It was a great way to give back to mom and dad for taking the grandchildren and allowing us kids to tag along. You have a lot of flexibility to design the adventure. Go for it, and you will be glad you did!