This is exactly my problem. I pay for 2 users at £10.99, I use one and the other is logged in at my (very elderly) parents house basically so mum can watch the Crown.
My parents are not internet savvy enough to be able to set it up themselves and I thought I was playing fair with Netflix with paying for two screens but I now find out I can't drop to one and add a sharer I still have to pay for two at my house and add a further sharer on at £4.99, so in effect I would be paying for 3 screens when no-one else in my house watches it.
I use it so rarely myself I think I'm going to drop down to 1 screen and just log it in at my parents and not use it at home at all.
Loss of revenue for Netflix but I can't justify £15.98 a month for one series of The Crown and maybe 3 or 4 films a year.