Yes, that was my point. You shouldn't have to, but Marriott has this rule about e-Certs in its
T&Cs:
e-Certificates
3. e-Certificates will be available when the Rewards Program Member is staying at the hotel.
When you order a travel package, Marriott issues a 7-day cert. I don't believe the cert needs to be in the account owner's name, but it needs to be in the name of the person who will be staying at the hotel, and that person may actually have to have a Marriott Rewards account. That's where I think the OP may be running into an issue. It appears the cert might have been issued in his name and the hotel wants to see him there to use the cert. The hotel has a point, so the OP should call Marriott, explain the situation and see if they will put the cert in his family member's name.
In the past the OP seems to have relied on the "he's showing up later" trick, but once the hotel questions this, you are out of luck if the first guest does not show. As I've said many times, this happened to me. Yes, you can usually get away with the trick, but the second the hotel pushed, you're stuck.
My intent is not to imply that the poster did anything wrong. My intent is to show that we all get used to a certain shortcut but when it goes afoul and a hotel decides to enforce the Marriott rules we need to have it corrected by Marriott, not the hotel.