question on using the companion certificate after cancelling card. This is the "newer" version where you must spend $6000 to get the pass.

I have the certificate in my account but I have cancelled the card 3 months ago. I want to book for my sister and her husband (which I heard you can do as long as the payment matches your account name). I have also heard you can use a gift card and the certificate will work instead of using an AS Card. But I'm not sure that I can do BOTH, pay via gift card for my sister and husband, does anyone know?