Adding Family member to a reservation

This is a random question and not sure how to word it to member services. We have a trip planned where my husband and I are flying in a couple of days before the rest of our party. We booked a studio at GF for those days before we move to a two bedroom at CC with the whole group for the rest of the week. We recently found out that my niece and her husband have also decided to drive down early and are staying at Coronado Springs those first two nights. I would like to add them to my GF reservation since it's just the two of us on that reservation. We aren't renting a car so my niece would like to be able to come and pick us up at GF to go do some shopping off property and to see our room at GF. They've never stayed there and are thinking about buying DVC. If I add them on our reservation will it mess up their ability to come and go from their room at Coronado?