DO NOT MAKE A BRITISH AIRWAYS HOUSHOLD ACCOUNT IF YOU WANT TO HAVE CONTROL OVER WHICH ACCOUNT THE POINTS COME FROM FOR A REDEMPTION TICKET.
They have a socialist system where they take from the account with more miles even if there is enough in the lesser account and even if the whole ticket is only for the lesser account holder.
They don't even ask you which account to take the avios from.
It's buried somewhere in their terms and conditions.
So now I'm left with 700 points short of enough points to book a ticket for the lesser account because they took just 700ish from that account and 8000ish from mine.