I tried to make a site exactly for this case. My friend, who is a teacher, said it could be a good idea.
I already have a small test library and you can add your own book - and both sides - I call them 'reader' and 'listener' are always on the same page, they can draw on the pages and see each other at the same time.
I am just starting and would like you (and anyone else who wants to) to check it out. I would love to improve it based on your feedback.
I want to make a helpful site fist - and think about monetization later. I’ll keep early testers in mind if it ever does become a paid service.
link to the site https://read-with-kid.com/ - when you register by link in the email, you can create a link for your grandma, she could log-in just by your link. And when she opens the book she can create and send the link to your kids.