Thank you for the additional replies!
When I suggested this to my sister, she said that her and my b-i-l stayed at the Yacht and Beach Club in 2020 and her sons had to pay for parking when they came over, but they were allowed pool access because their names were on the reservation, however their sons girlfriends were not allowed pool access.
I guess with things in a near-constant state of flux, we won't know for sure until we get there.
I did change my reservation from 2 guests to 4 guests for lunch at Sanaa on the day they would be coming over, but I'm not sure how they would prove they were on the reservation without me linking them in
MDE.