Comment by jackson1way

You could also customize the notification sound for incoming messages in whatsapp and mute (or just use a short plop sound for) anyone else for grandma. Now grandma can focus on learning to use only one app for all her grand children and will find all the pictures from all her relatives in one place and will more likely be able to even forward pictures to other people on her whatsapp. Assuming Grandmas in their 80s.