Depends on when you're going. If you're going during the summer high season, they may not be able to go to the beach house or pools with you.
When the resort is filled to capacity, they often check for room keys at the pools. Now, if you have a 2BR and don't have 8 people in your family, you CAN request a maximum of 8 room keys so that they will be able to produce one if asked. You might want to have that as a "beach" day, rather than a pool day just to avoid any problems. You might have to be your own shuttle if everyone won't fit in one car to get there, but at least they will be able to spend the day with you!
There are no day passes available for purchase or otherwise.