You can change the ID by creating a new ID. When changing to the new ID, 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 a new
Apple ID – Create
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
For the iPad, make a backup of your current device and then restore the backup to the new iPad. To restore any data synced to iCloud, on the new iPad, sign into Settings/Your Name/iCloud using the same Apple ID used to sync the data to iCloud, and turn on desired syncing.
Transfer content from an iPhone, iPad, or iPod touch to a new device
Quick Start to transfer data from your previous iOS device to your new iPhone, iPad, or iPod touch
Backups – Choose Method
Back up your iPhone, iPad, and iPod touch
Backup - Restore your device from an iCloud or iTunes backup