Extremely difficult to add family member to premium family account

[rt2015]

I signed up for the Premium for Family account and am now attempting to add my partner, who has the same address. I've sent him an invite twice. When he clicks the "accept" button, he's taken to a page where he's asked to sign up for a family account *under his own name* and not mine. In addition, he's being asked for payment details. Also, there's no place to redeem the code that came with my invite to him. I merely want to add him as a family member. Is there a simple way to do this?