My spouse has an icloud account and is using approx. 50 GB . We want to move this info to a family sharing account. What do I do to cause the transfer from the personal account to the family account

Make sure the spouse is part of the family and that one family member has a higher level iCloud+ storage account (or an Apple One family subscription) so it enables family sharing on that subscription.

Relevant links:

Click on this link to learn how to 'Set up Family Sharing' --> Set up Family Sharing - Apple Support

Read the section: "Invite people to join your family"

Upgrade to iCloud+ - Apple Support

Bundle Apple subscriptions with Apple One - Apple Support

Share iCloud+ with your family - Apple Support