Apple One family icloud storage

I would like to know that if I subscribe a Apple One Family, Can I manage the iCloud storage like sharing with each family member 40GB of storage? (with a family of 5) So every one can have their own privacy.

Sharing is rather the point of Family Sharing. Details are here.

About half-way down this text is especially relevant to your question: "When you share a storage plan, your photos and documents stay private and everyone keeps using their own accounts with iCloud – just like when you have your own storage plan. You simply share the space available in the iCloud storage plan with your family members, so you only have one plan to manage."

You have a few options according to this document under the heading 'If the iCloud storage included in Apple One is less than your current plan' it states"You keep both your current iCloud storage plan and the iCloud storage in Apple One". So you might wish to increase you own storage plan to the 2TB plan. Or you could work out with your family participants that they don't upload documents, photos etc to the 200GB space.

Mathematically that would be correct for a 200GB storage plan but it doesn't work that way. Every member's space is private and members can use what they need up to the cumulative total of the data storage plan.

Go back and read this thread and Apple's support document I linked above.