You can make video calls via WhatsApp as well as Facebook Messenger, and it has Amazon’s Alexa built in.
If you have an Amazon Prime account, an Alexa Show can play Amazon Prime videos.
Fire HD tablets have Alexa, so grandma would be able to use the same video calling system as with an Alexa Show.
See below…) The Fire HD also has the advantage of providing tablet apps, so grandma could do her emails, browse Facebook, play games and other things.
If grandma didn’t want to use FaceTime for some reason, iPads support many other video calling systems, including Zoom Cloud Meetings.