What you will need to buy for them is the 10 day certificate w/ no add ons. Then when they get to the park, they can go to Guest Relations to turn it into a regular pass (they will both need picture ID's), and at that time, if they want to add on anything like the hopper option, no expiration option etc, it will be up to them. I think it is very generous of you to purchase the basic 10 days.
Hope they have a great time!