My suspicion is that the Chitchen Itza event was actually required to start bringing over the Outsiders to help the Formor. A fairly consistent part of the magic system is that the mood or atmosphere of the world matters. Dead Beat had Cowl messing with Chicago to "prime the pump" and Battle Ground showed that the fear of Chicago affected the spells cast during the battle. Since the big spell at the end of Changes affected so many people who weren't the Red Court, I suspect that certain spells would have been easier in the wake of the bloodline curse. I bet that it would have helped summoning an Outsider that is described as a peer to Mab. After being summoned, the Walker then helps the Formor assemble their forces and/or knock down some one like the king of the Tuatha as payment. It then starts assembling it's forces to assault Demonreach.

As for what the Outsiders get out it, beyond a Walker that gets summoned, is more chaos. Mab, Odin, and Uriel are chief forces in alliance for the current order among the natural world. Mab and Odin also established the Accords. Eliminating the Accords could pull away some of Winter's forces from the Wall and a massive global war would kill a lot of the people who could stand up to the Outsiders after they breached the Wall.

I hope the fact that Lara and Harry share a brother, but aren't technically related, is a source of joking or tension in 12 Months. Lara grew up when the Hapsburg chin was still a good thing and she's had way more incestuous sex than with her half-brother's half-brother (thanks Papa Raith). She almost certainly won't be bothered by this relationship to Harry but he probably will.

My personal favorite explanation is that the Council allows for flexibility in matters of self defense or defense of one's interests. We know that they allow for killing via magic in defense and I wouldn't be shocked in relatively minor breaks to some of the other 6 would be allowed too. One example is Dresden's wards that "suggested" people skip his bolt hole. Those were a gray area but, since they didn't cause permanent harm or major effects to the timestream and were in self defense, so they were fine. The mind fog grenades that Butters had only worked temporarily (if I remember correctly) and he got them while trying to help the humans of Chicago. My suspicion is that most Wardens would have let Butters off with a warning but tried to kill/capture Bob.

In defense of the OP, I suspect that honest-to-goodness deep love would inspire courage, hope, faith, and anything else that Malvora and Skavis would hate. It may not instantly cause them to be burned like a Raith but, since we know the White Court like weak prey, I bet it would cause them to not target people in a solid relationship. Maybe it's just my sappy side talking but I like to believe that real love inspires courage and hope. 

I listened to an interview with Jim that was mostly just writer-talk and his history (linked below). It did have some lore questions and someone asked about why Justine didn't mess with the island in Cold Days. His answer was "She wasn't possessed by Nemesis them". It was fascinating and out of left field. In Battle Ground, when Harry asked how long she had been Nemfected, she said "Mortal time is such a limited concept. A few years. Ever since she became close to Lara". That heavily implied to me that she was Nemfected all the way back in White Night because that's when she became Lara's assistant. With this WOJ, her statement almost certainly means an emotional closeness. Maybe Lara found out about Thomas and Justine resuming their physical relationship and it led to Justine and Lara becoming sisterly? I don't know but that's my best guess. We better get answers in the next book though.

Interview: https://www.youtube.com/live/NaAjmJWxnBo?si=t4GTFBqNV_KzInp4

There's a couple of good explanations here that I think undermine your theory. First, Jim changed his mind or only meant that Harry isn't getting any more children. He does have two of them counting Bonny and Harry does count her. Second, Justine did get pregnant and just cheated on Thomas. It would be relatively easy for her to do by Nemfecting her bodyguards and maybe having one them do it. She could have easily started the process right around Skin Game and conceived by Peace Talks (it's about 1-2 months between those two books). She could force Thomas into doing the mission right away so he couldn't reasonably ask for a paternity test by saying "Hey Thomas, I've been possessed. I've been skipping my birth control pills, taking medicine to help me ovulate, and poking holes in the condoms. Do what I say or I'll hurt your baby." I bet that would work on Thomas considering he accepts he's going to become a father in the first chapter of Peace Talks. 

Either way, there's a couple of ways to fit Justine's pregnancy in with the WOJ you mentioned and with the book canon.

Jim has said that any fight between Mab and Titania would almost definitively be a toss up. I think the Summer Mother in the visit to the Outer Gates in Cold Days talked about Mab and Titania's power being equal. My memory is that Mab is personally powerful and controls vast armies to protect the Outer Gates. Titania is equally powerful with a much smaller army, relatively speaking, as a check on Mab. Mab can't take over anywhere else because Titania would personally kill or maim her if Mab tried anything squirrelly. My strong suspicion is that the Ladies and Mothers are equally powerful as well.
I bet any of the Faerie queens could do remove or greatly restrict the Whampire demon if their job description allowed for it. I don't know if any would. My bet is on Mab and Titania's job giving them the power to do it solely because Mab threatened to make Thomas the Winter Knight and I don't think she would want competition for control or influence on Thomas.