That does not seem defamatory to me, especially with the evidence available to support your seemingly reasonable belief.
My advice: consult with a Nevada attorney who understands this area of the law and heed his / her advice.
In the meanwhile you might want to make hard copies of any posts from Alan or his son which would support your argument.
I suspect douchedawg lacks the legal experience to file and successfully try a hotly contested defamation action; hell I doubt he's ever had such a case.
When you consult with an attorney ask his / her thoughts about what your legal options are if they file a suit and secure your IP address via subpoena and use it to get your name and address but then never go through with the suit, i.e. if he just "drops it."
That would indicate abuse of process if he only used the suit to get your name and address; given that these clowns have pursued you and this info fairly relentlessly you may have a counterclaim for abuse of process.
Whatever, time to lawyer up.
Oh, how did you learn his name and that he's willing to represent Alan for free?
If that is what he wrote make a hard copy of it and use it if he ever makes a claim against you for an award of attorney fees.