All members of a Home subscription share a pool of storage space. The size of the storage space available for the whole family depend on which Home subscription you have.
Each member can upload as much data as they want, but when the total storage usage reaches the limit of your subscription, the account is full. If you want more storage, you can upgrade to a Home subscription with more storage space. The available subscriptions are Home 1 TB, Home 5 TB, Home 10 TB and Home 20 TB.