Have 2TB of iCloud storage-family shared & iPad saving to iPad storage and not iCloud and iPad unable to back up

I would like you to realize and know one important thing and that is that there is NOTHING that you can do to increase the physical storage capacity of your iPad. Your iPad's storage capacity will forever remain the same as the day you bought it. 

You can purchase ➔ iCloud Storage from Apple where you create and save your iPad backups and synch (Not Store) your Messages, Photos, Contacts, Calendars, Notes and Reminders. Note that iCloud Storage is NOT an extension of storage capacity of your iPad. Just wanted you to know some facts.

Having said that, you can choose to Optimize Storage on your iPad for all the Photos. What this action will do is store your original quality photos on iCloud and a small size photo on your iPad. This takes up less space on your iPad while maintaining the actual size on iCloud. This will free up space on your iPad while making good use of iCloud. If you would like to try this then open Settings ➔Photos ➔ Optimize iPhone Storage : Ensure that this option is chosen and has a checkmark on it.

Axel F.