Although you cannot transfer American Express Membership Rewards between two different Membership Rewards accounts, you can basically share them by transferring your Membership Rewards points from your Membership Rewards account to the linked loyalty account of another person. Yes, you can do this despite the fact that the program rules state:
“Points are not your property. You can’t transfer points to any other person or program account.”
So how do you get around this rule?
Transferring your points to an authorized user’s loyalty programs-Amex allows you to transfer your Membership Rewards points to the loyalty programs of authorized users of your account as long as they have been an authorized user for at least 90 days.