The couple have a thirteen year old son. I think it’s a good possibility one of his peers might be involved. If some thirteen year old boys are fighting, sending threatening letter to parents is about their speed.
I still don’t see the first letter. Therefore, as a completely amateur and uncertified detective I believe this is a ruse to cover up their part in the Lindbergh baby kidnapping. As an outside possibility it’s a prank by some kids.
I still say it’s some southerners from Wolfe Island. After all, they have to take a ‘fairy’ to get to Kingston. That probably pisses them off.
I’m going with “lone nut”. Self-hate-crimes-hoaxers tend to overshoot (e.g., montag’s story, whatever the fuck this was). “We will hunt you down and shoot you with BB guns, and we can assure you it will sting!” doesn’t quite fit. I know it’s Canada, and I hear your people are polite, but still.