For the question about moving one segment to your wife's account so she pays the Avios rather than you, the only way I can see this working would be to call BA, have them split the PNR, cancel your wife's booking (paying the $55 charge and potentially an offline service fee too), and then for your wife to make the same booking that's just been cancelled but using her Avios. This assumes, of course, that there's Avios availability in the cabin and on the date you wish to fly. That isn't guaranteed. Cancelling an Avios booking doesn't mean that the seat will go back into inventory to be rebooked using Avios. It may. It may not. If it were me, I'd just leave things as they are.