Hi Mary,
I think your question is answered in the "Borrowing, Banking and Credit Cards" section.
As an aside, I did what you did, but I explained to UB what I was doing they kindly paid the tax for the card that was closed for the part of the year we had it.
The second card user has to be given explicit authority to make enquiries on the account. This takes the form of a letter from the primary card holder authorising the second card holder.
Also for some reason my partner is unable to book flights on the RyanAir flights using the details on the second card. But is able to book flights using the details on the first card.
ajapale