I think what makes it difficult to teach elders how to use a smartphone is their general lack of interest. They seem satisfied with their small feature phones and do not see the need to use a smartphone. The first thing is to arouse their interest in using a particular feature, and they'll learn it faster.
Imagine the extent your dad went. He got a notebook for "phone lessons". That's probably because he was really interested in using a smartphone. We had a problem convincing my mum to use a smartphone too. As you said, the game-changer was WhatsApp video calls. She was too happy to see my siblings during video calls. Now she prefers video calls to voice calls and we have to keep crediting her line with data weekly.
Thanks for this post. Quite interesting.
This is very true. We need to make them interested first if we want them to really learn something. Thanks for reading and I am sorry for my late reply too.