Scavenger hunt to find iPhones for Christmas

My sisters are both getting iPhones for Christmas and I want to send them on a scavenger hunt to find them! Please help with ideas of how I can set up the clues!

In the middle of the night make sure there asleep then go and put notes in front of them like on there wall or there desk then let it say go to the back yard for your next clue write down another clue like x is where your prize is buy a tresure chest and burry it and paint a red x on the dirt or grass then they will open it then ya thats pretty good

Ok. When their asleep. Wrap the first clue in a box so they'll read it. When they go to the place to find the next clue, hide it lower then their eye level. Then send them digging through a clothes hamper and the next clue is in there. Then they find the iPhones under a bathroom sink. I would do this order:

-In the box
-In the living room somewhere
-In a clothes hamper in garage or laundry room
-Phones are under bathroom sink