Thanks, PanGalactic, for your reply.
I have been thinking of creating a HHA for hubby & myself - both members reside at same UK address, as well as applying for an Amex card (again - last time they rejected me because I had no history, having only moved here for less than 6 mos).
I have created an account for myself with Avios.com, but so far I have not accrued any Avios on it as I have directed all my Avios to BA instead. So, you say if I have an account on Avios.com, then I can transfer my Avios points from BA to it, and book an award flight for my sister (who is living in the US)? Yes, I live in the UK now, but my sister lives in the US.