You can’t put on the same ticket but you can buy for the other couple on their behalf. However once you “transfer” it to them to book, you can’t transfer back so by the T&Cs if it’s later canceled you can’t get it back (though YMMV with COVID waivers and what not).
The T&Cs require your AMEX to be used for booking the ticket (though in practice historically I’ve been able to use any AMEX in my name — notably the AMEX Plat for the 5x MR) so you will likely have to actually complete the entire transaction and then just get reimbursed from him offline.