So why does this happen? Double charging?

a) A family member is added

b) They don't already have a storage plan

c) Their name appears in the iCloud Storage list of people sharing my 2TB storage plan (with 1.9TB free)

d) But the iCloud Storage list says they are not using it

e) Then that family member is invited to purchase themselves a storage plan on their device by Apple

f) Now I have to pay twice a month for 2x 2TB storage plans