Give them something to motivate them to get up. When I want my housemate to get up I make him pancakes (and he's 28!). You could have a rewards chart where they get a sticker each time they get up early, culminating in a reward when they get a certain number of stars. You can also compromise with them...allow them to get up a little later than on school days but not too late. Or you can plan activities where they need to get up at a certain time, for example going to a friend's house or a movie.