The terms and conditions state:
"
- A Member may redeem a reward night for immediate family members (spouse, partner, children, parents, in-laws, brothers and sisters) only. Immediate family members can use the free night even if the Member is not occupying the room.
When booking a reward night for someone other than yourself, be sure to ask the reservation agent to include the name of the guest in the notes field of the reservation. When booking a reward night through your online profile, be sure to include the name of the guest who will be staying in the room in the “Special Request” field."