Does Apple refund prorated cost to people who cancel their personal storage plan to join family plan before end of billing period? Thank you so much in advance, and sorry if I made any typos. English is not my first language.

My siblings and I (4 people) are using their storage plan individually and each is paying $2.99 per month for 200Gb. Meaning we are paying almost $12 a month. Now we want to include our mom in, and save some money, so we would like to upgrade to the family plan at $9.99 per month for 2Tb. I understand that one of us will have to upgrade their plan and then share the plan with the rest of the family, and Apple will charge that person the price of the higher tier plan, minus the prorated cost of their previous plan. My question is, will Apple refund the prorated cost to 3 other people who will cancel their personal plan to join the family plan - or they will be charged for the entirety of the billing period just like what usually happens with other Apple services such as Apple music?
According to Apple:


  If a family member is already paying for their own iCloud storage plan, they can choose to switch to your plan or keep their own and still remain part of the family. When they switch to the shared family plan, they get a refund for the remainder of their personal plan. They can't keep their current plan and use the shared family plan at the same time.