Being a senior myself, albeit tech savvy, I think the main thing to teach them is to not be afraid of it. If they have young (5 - 8) grandchildren, one way to do this is to combine the grandchild with the grandparent and encourage them to teach each other, especially since you already have that "mobile petting zoo". The kids will not be afraid to try stuff and the grandparents will enjoy interacting with them and want to learn enough to stay ahead of their grandchild.
Another thing might to introduce them to Facetime on the iPad, or Tango on the Android or IOS. It's a way for families that are far apart to see & talk to each other. BTW there is a "Facetime for PC" app. look
here. So they can do Facetime with a PC to/from an IOS device.