how do we change the organizer for family sharing?

You have to disband the current family and set up a new Family group with you as the organizer.

Leave Family Sharing - Apple Support --> https://support.apple.com/HT201081#disbandgroup

Set up Family Sharing - Apple Support --> https://support.apple.com/HT201088

From: https://discussions.apple.com/thread/252984600?answerId=255602228022#255602228022

"If there are children under 13 years old, the new organizer needs to leave the existing family, set up the new family, and then the under 13 years old children can be transferred to the new family. Then disband the old family and join the new family."

Move a child to another group using Family Sharing ---> https://support.apple.com/HT201080

https://support.apple.com/HT201088

"Remember, you can only join one family at a time, and you can only switch to a different family group once per year." June 2021

https://www.apple.com/legal/internet-services/itunes/us/terms.html

D. "Family Sharing Rules: You can only belong to one Family at a time, and may join any Family no more than twice per year. You can change the Apple ID you associate with a Family no more than once every 90 days. All Family members must share the same Home Country."

See the document about what happens when you leave FS. In your case though it will only be for a short time. The main concern is if you use Apple Music because then you may lose content unless you take out short-term individual bridging subscriptions that will let you keep content (and playlists) during the transition.