Add your family or friends once your logged on. You can list them as passengers and get them seated together as well.
I bought 2 tickets for my friend and his wife - bris bankok return - without a problem. You just need their passport and full name DOB etc.
From the site :-
"How do I make redemption bookings for my nominees?
If you already have an existing list of redemption nominees, you can redeem flight awards for them by visiting the Online Redemption Booking page. After selecting the origin and destination cities, travel dates and the number of passengers in the travelling group, you will be asked to choose your preferred flight(s) and to indicate whether you are part of the travelling party.
If you are redeeming for your nominee(s), you will then be asked to select the specific nominees for whom you would like to redeem the award ticket for, and their details before proceeding to make the relevant payment.
For offline bookings, please complete the Reservation and Miles Top up Request and fax your form to KrisFlyer Membership Services.
If you do not already have a list of redemption nominees, you can nominate up to five family members or friends here (
https://www.singaporeair.com/saa/en_UK/Account/KFORGNAdd.jsp) "