Apple One Family iCloud storage question

You get 200GB total.

Each family member can use any of that but the total for all members cannot exceed 200GB.

If you need more, the following from What happens to your iCloud storage plan when you sign up for Apple One - Apple Support may help:

After you subscribe to Apple One, you can buy more iCloud storage if you need more. With both Apple One and an iCloud storage plan, you can have up to 4TB of total iCloud storage.