Can I add a guest once I have booked my week in my name. I don't see an option online - do I need to call them?
Call the specific resort you made the reservation for. Just tell them you want to add someone to the reservation so they can check in as they will be getting there before you do.
That being said, it's easier just to put the reservation in their name to begin with.
There are a few caveats to this method. If it is a primary member only resort you will not be able to add someone to the reservation. If it is an affiliate resort you also may not be able to add the name to the reservation. It should not be a problem at a Diamond managed resort that has no restrictions (about 98% of the Diamond resorts).