I'm unwashed and have a OCD old man too, but he mostly keeps his trap shut about religion in my presence now.
What I did, was get him to agree, one king at a time, quoting WT rags, to all of the lengths of the reigns of each of the Neo Babylonian kings, then added them up one at a time quoting the rags again, getting him to agree that the calculation was correct for every one.
When I got to the end of the calc and he realised he was in the crap, he asked where I got my information from. I reminded him that I had just quoted all of it from his own rags and that he had agreed. He asked why is it important? He was just trying to change the subject by finding anything he could accuse me of. I just told him that I would discuss that after he shows me his list of kings to show where the mistake is.
He has tried every excuse he can think of to get out of showing me where the mistake is. I ignor the lot. If he tries to weasel his way out of it using some trick he has accused another religion of, I pounce on the double standard. He has to feel guilty that he hasn't answered my question until he gets his arse into gear and answers it.
He will wait months, or years, before he forgets and talks religion again, but I have 'King List' tattooed on my forehead and he gets headbutted with it at every opportunity he gives me. I refuse to talk about any other WT topic. If he wants to save my arse from his killer god, he has to answer MY question, and if he doesn't get around to it smartly and his WT god kills me, that's his fault for not answering MY question promptly, with honesty and integrity, and without trying to bully me into some shonky explanation by a bunch of old farts in Brooklyn. I don't follow men.
Guilt, guilt, guilt.
Never answer his questions. Never let him change the subject. Never change the subject unless it is to talk about something really important, like fishing, sport, gardening ....