So you've set something like that up for your grandparents and they have no problems using it? Otherwise, this is just Monday-morning quarterbacking.

There are many ways music could have gotten on the iPad. You can purchase music from the iPad. Or you can enable manual music management so that any computer with iTunes can copy music to the iPad. Or it could simply be that Marco synced a bunch of music to the iPad and his grandpa never changed the songs.