Since my point was that evidence did in fact exist of Loghain's culpabiliity in betraying the king, I think I've proved my point. There is evidence.
Apart from that, I brought up Anora not because her imprisonment was unreasonable, but because if Loghain didn't trust Howe implicitly then he never for a moment would have had Anora stay imprisoned by Howe. He would have removed her from Howe's custody as soon as his captain could ride across town rather than leave his only child, and the only slight thread of legitimacy to his ursurpation in the hands of a man he didn't trust. No interpretation of the text that suggests that Loghain had a problem with Howe withstands examination.
It's remotely credible that Loghain didn't intend to kill Cailan until the moment he saw the signal and realized that he had an excuse that might pass muster. It seems much more likely that he decided not to come during the planning meeting when Cailan threatened once again to call in the Orlesians. It's not certain that he intended to kill Cailan at all before then. It could be that he was just murdering Bryce and Eamon because of their Orlesian ties and potential influence over Cailan, figuring that Cailan was such a flutterwit that he could cover what his agents had done and steer Cailan away from Orlais now that nobody else would have access. That would be an underestimation of Cailan I think. Cailan wasn't especially bright, but he wasn't quite that controllable or quite as stupid as he seemed.
Though I would tend to agree with most of your points regarding Loghain's trust in Howe and his culpability, there are a few interesting tidbits about Eamon, from reading WOT vol2 that I think provide a more precise view of Loghain's motivations:
-"Eamon is as loyal as a Mabari" Maric once proclaimed. So Maric trusted Eamon and while Loghain and Maric often disagreed on things, I would think Loghain Loghain would still respect another lord who also fought in the rebellion.
-It's Howe and Maric who disapproved of Eamon's relationship with Isolde. I can't imagine Loghain would particularly approve, but it's Howe who make snide comment about Isolde during a banquet:"It seems our secrets are safe with Eamon, unless the ennemy has pretty ears"
-You learn he wanted to instill Ferelden pride to his son. "The war with Orlais had forced Eamon from his country, and he was determined to impress upon his son the glory of Ferelden".
So I really think Eamon's poisoining was really more Howe's work rather than Loghain's (though he must have agreed to it, for pragmatic reasons). I keep thinking Loghain saw an opportunity and made a pragmatic decision at Ostagar but didn't plan the whole thing ahead.
What I mean is that I think Loghain disagreed on some things with Eamon, but didn't see him as an outright traitor sold to the ennemy (same for the Couslands).
A: I can't help but feel that many of the assumptions regarding Ostagar that seem to influence this paragraph are called into question by points I've raised that you've yet to actually refute.
B: I personally view marrying Celene in favor of Anora because of Anora's perceived infertility, with Celene being even older than Anora and coming with the "joining our kingdom with the one most of the sitting nobles were once tyrannized by" baggage, as evidence that Cailan was far dumber than he seemed.
B. Just a precision. We are told in the game Anora is approaching 30 in Origins without further precision. And Cailan was born in 9.05, so he is 25 at the time of Ostagar. There isn't any mention on Anora's age in WoT, but we know she was practically raised with him. And Celene is 26 in Origins. So even without knowing Anora's birthdate, I would imagine all three are fairly close in age, with Anora likely being slightly older.
Doesn't change his foolishness. What I keep questioning is the inconsistencies of that plot with some lines in The Masked Empire. Could likely be writers not communicating with eachother on that point.