The following thread may be useful, as it discusses the same situation as I understand it.

https://www.flyertalk.com/forum/brit...d-account.html

My understanding is similar to yours - the HHA in and of itself does not allow you to access your wife's Avios to transfer them to Iberia. I believe that must be made as a separate person to person Avios transfer (from your wife to you) so that you have the required amount - effectively the same as if the HHA did not exist.

There are limits - 27,000 per person per year, and there may be costs as well. It is free to Gold members and above, but will cost if you have a lower status - seems to be £15 per transfer at the moment

https://pgt.shopping.ba.com/?utm_sou..._content=Share

Costs:

https://pgt.shopping.ba.com/resources/pricing-share