You can't split an Apple ID. You can't transfer all data. To share Messages, the existing conversations will probably be lost on a new ID, but you can both sign into Messages using the same Apple ID. You will need a 3rd party app/application to keep your contacts in sync. For Photos, you can create a shared album using iCloud.
There may be some data loss, but you can minimize it. If syncing photos with iCloud, ensure Optimization is turned off in Settings/Your Name/iCloud/Photos and/or in Photos/Preferences/iCloud. Then make sure full resolution photos are on the device/computer. When signing out of iCloud, if asked whether you want to retain data, choose yes. Messages conversations will be lost if they are addressed to the ID. See the article below for other places that the old ID should be removed. See Winston Churchill's response in the below discussion. Also set up Family Sharing to keep access to your apps/purchases.
Apple ID – Create
Apple ID - create a new
How to transfer all files from one iCloud account to another
Apple ID email address or password - What to do after you change
Family Sharing
Family Sharing - Set up
Photo Sharing - iCloud
