There was a discussion about this recently on another thread and it isn't possible (or wasn't at the time of that thread). The only way to do it is for the other member of the household account to gift the miles to you (and pay a price to do so), they can then be transferred to your Iberia account. If you try to transfer miles which are in other HHA members accounts to your IB account, you'll get an error and a link to the terms and conditions, although it doesn't specify which term has been broken.