I really hope it didn't sound like I was just dumping all over your efforts there FF2005, or patronizing
Your letter touched a few particular notes. Speaking from personal experience (on the receiving end of this kind of thing)...in my dad's dying letter to me he expressed some of the same old school traits.
First a bit of background - we are both engineers/scientific by nature. In his life he was afraid of looking weak/being vulnerable, showing much emotion (he had to protect his pride, stiff upper lip etc)...but most of all, he was always consumed in some form of activity (from work 24/7 to hobbies) to the point where it seemed us kids didn't matter that much. Eventually he got so ill that the life was sucked out of him (couldn't show interest in anything around him). I know in my mind that he did care, but just didn't feel it as a kid. I don't moan about this or use it as an excuse today (e.g. "woe is me" LOL), but it is noted in my head. Bottom line, I really didn't care about my fathers "wise counsel", as a kid I just wanted his genuine attention.
Anyway, enough of the sob story ....fast forward to my dad's dying letter - in it he wrote some courtesy notes about being proud of me, but the resounding parts were where he pleaded with me to "come back to Jehovah", and how he wished I "used my talents to their fullest capacity". The take home notes I got from this letter was that I was doing something wrong and he wasn't really proud of who i am (what my life choices were, what I decided to believe in etc). Imagine getting that as the last communication from your father. I don't want that for you, or your kids! (or anyone else for that matter, not when it can be helped).
The over-riding principles are the same no matter which side of the fence you're on. For a JW to receive what could be the last communication from their father telling them that their life choices weren't approved of = the same thing as above for me. It's dejecting and too close to home to just ignore. No matter whether you believe their religion to be a pile of garbage, it's still attacking their personal choice (albeit coerced via cultic tactics).
A more ideal father-son letter would include:
1) Forgetting pride & guidance. Just be human. As funny as this may seem, be a friend more than a father.
2) Be personal, specific to them. Be interested in their life/character.
3) Reminisce about the short time you spent with them as kids. Tell amusing stories they may not remember (be specific again to each one).
Steer away from trying to explain yourself (or over-emphasizing the "why's"), it often just brings attention to it in a bad way.
Really hope this helps!