> Many of my older extended family members have a single email account shared by a husband and wife. Or in one case the way to email my aunt is to send an email to an account operated by a daughter in a different town. Aunt and daughter are both signed in so the daughter can help with attachments or “emails that go missing”, etc.
As usual with the "personas" scenarios, people creates their unrealistic scenario (just like when talking about UX or design). These personas you are describing will probably fall back to low-tech methods in most of the cases, they won't fail to take a plane because GMail locked them out due to unusual activity when they are trying to show the ticket QR in the airport. They will just print it (or have someone print it for them) beforehand.
> The seaman in this scenario has a smartphone with the email signed in. It’s also signed in on the family computer at home. Both the wife and him send email from it. Maybe a kid does to from a tablet. This isn’t that difficult.
You just missed to add that they use their shared email to communicate between them by using the "Sent" folder.
To be more realistic, the seaman right after buying his Android phone will create without realizing a new Google account because he doesn't probably know that he could use the email account he is already using at home.
But, enough with made-up examples to prove our own points.