At arby2008's suggestion, I called Apple Support. SEVENTY phone and desktop sharing minutes later, I can tell you there is no change to the situation.
The technician has now "verified" that I (we) have a problem. He has "collected information" and esclated this to Apple Engineering.
He watched as I created events in my calendar and toggled back and forth to my husband's email to watch the notifications come in. We tried it in the reverse (creating events in my husband's calendar and looking at my email: same situation). We tried turning ON the "send email" switch box to see if the controls were just reversed (they're not - it sends email either way).
The only way to stop receiving the notification emails is to stop sharing for now.
I did mention this support discussion and he saw the thread open on my computer during desktop sharing so he knows I'm not the only person affected by this.
It's not good news - but at least it's information.