How do I share iCloud storage with my wife who has a separate Apple ID?
What do I have to do to share iCloud storage with my wife who has a different Apple ID on her phone and computer? Also how do I cancel her current iCloud storage plan?
See the instructions in Share an iCloud storage plan with your family - Apple Support
Regarding cancelling her plan, see the following from the same link:
When you share your iCloud storage, any family members using the free 5GB plan are added to your family plan automatically.
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.