Restore from backup with new Apple ID
As fsb mentions, the photos are all tied with the Apple Id which is associated with the iPad. So, here is what we did


Connect iPad to PC / Mac
Copy all of the photos from iPad to PC / Mac
Upload photos to Google Photos associated with Dad's gmail
In the new iPad, sign in with Dad's email address (this can be the same gmail account as above or a new account). 
Download the Google Photos app and sign into it with the gmail mentioned in step 3.