Again, I thank you all for your advice. The perspective on my MIL was particularly insightful and, it lead me to information on Narcissistic Personality Disorder; it made for alarming reading (like a personality profile of my MIL). I need to determine how to manage that both short and long term.
This is a more comprehensive update than I provided before (little time until now). I recently gave my wife a list of demands (timeline, poly, post nup, STD test, etc.) and advised that, if she didn't agree I would be leaving on a trip for a few days, during which she would receive divorce papers. She took them for discussion points (despite my disclaimer these weren't for debate) so, I started to pack my bags. During this time she contacted her parents, who arrived while I was putting on my coat. My wife seemed to have a panic attack so, I had to try to calm her.
When my in-laws arrived I told them I'd briefly explain what was happening so they understood my position. I also wanted to take this unplanned opportunity to attempt to balance any distortions of the truth my wife had told them - more for me than them (I've got to try where I can so that, if the marriage ends, I've done all I could). In brief, they claimed they weren't aware of the full timeline of events/ extent of the deceit and, how supportive I'd been over the past couple of years (my wife had only conveyed negativity about me). My father-in-law seemed to warm to my perspective...then had a panic attack. Afterward, (we were all still together in the same room) he said that he couldn't understand how I could ever trust my wife/his daughter again (I've never seen him emotional -- he was a wreck), whereas my MIL pretty much stayed silent. My wife initially offered counters to my position, then capitulated, admitting that, in hindsight, she communicated an inaccurate impression of me.
My wife then raised the matter of my demands. Again, my MIL was silent, whereas my FIL tried to understand (he struggled with the polygraph, thinking it was extreme). I grew exasperated (but remained calm) and told them that, they don't have to understand and, diplomatically, that I'm being civil taking the time to explain and that these are essential steps to me being able to work toward a foundation of trust. MIL then made a comment about a positive STD test not proving anything other than what someone is infected with, not where they got it from. I countered that, I know I don't have HIV as I recently had blood tests (for a chronic illness) and, HIV is done as routine. If my WW has HIV for example, it's important I know and, is a possibility given the AP has a Tinder profile and frequently visits the far east for work and, for all I know they had unprotected sex. FIL bursts into tears at this point. I end discussions telling them we can talk in future but it's been a long day and there are things to do.
I return to packing my bags. My wife breaks down at the front door as I'm about to leave and...my eldest son appears at the top of the stairs. My wife says she'll meet all of the demands and begs me to not leave. I go to my son, cuddle and put him back to bed and, explain to him that his mum was a bit poorly. I didn't leave. I told my wife to start working on the timeline once she was composed. She did.
Timeline is now done and, I'm creating questions for a poly. I've also been in touch with the AP's wife, who confirmed they were trying to reconcile and, has clarified dates and times of events I know (she has her sources).
I hope that wasn't too garbled.
[This message edited by BSPheonix at 5:43 AM, December 5th (Thursday)]