Q: iCloud won't synchronise with iPad and iPhone

Have you checked how much iCloud storage you are using lately?   If you run out of iCloud storage, your device won’t back up to iCloud. New photos and videos won't upload to iCloud Photo Library. iCloud Drive and other iCloud apps won't update across your devices. And you can't send or receive messages with your iCloud email address.

Manage your iCloud storage - Apple Support

Well, all I can think of is to contact Apple iCloud support for assistance.

Can you "easily" make an appointment at the Genius Bar at an Apple Store near you?  I said easily because I doubt there is much else they can do for you, but at least you would be talking face-to-face with an Apple representative.

https://www.apple.com/retail/geniusbar/

Try Settings/iCloud and slide off syncing. Wait a few minutes and then resync.

Have you tried signing out of iCloud and then sign back in?