Need to get 4TB of iCloud storage

Jerry Zurek wrote:

I believe that if I cancel Apple One Premier from Account B and buy it with Account A, Apple will cancel my iCloud storage on Account A and replace it with the 2TB from the new Apple One Premier.

When subscribing to Apple One, it will retain the existing 2TB during the Free Trial.

click here ➜ What happens to your iCloud storage when you sign up for Apple One - Apple Support

But you are then free to re-purchase 2TB with Account A, to add to the 2TB from the Apple One subscription for a total of 4TB.

If you need more iCloud storage

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

Could I then purchase 2TB iCloud with Account B and then apply that storage to Account A with the result that Account A will have 4TB and Account B will have just the base plan?

No. You cannot merge storage plans from different Apple IDs.

Subscriptions are currently being purchased with Account B. I am not sure if I need to start using Account A for subscription purchases.

Thank you for your help.

That's up to you. Not sure why you have 2 accounts to begin with.