Huh? I haven't read any of the books, but...Howe made a power play to take back what he felt the Couslands had taken from his ancestors.Loghain left Cailan & Co. swinging at Ostagar because reasons. He wanted to preserve the rest of the armies instead of having them all slaughtered, he didn't believe it was a blight, he believed Cailan was conspiring w/ Empress Celine and would dump his darling daughter - take your pick.The 2 of them - Arl Howe & Loghain - did conspire to assassinate the Warden.Since they're fictional characters, I'm inclined to believe the authors about anything not explicitly demonstrated in the material.
Gaider's stance was that Loghain and Howe were not involved in a conspiracy against the crown and the Couslands, and that Howe's move against the Couslands just happened to coincidentally occur at around the same time Loghain commits regicide.
The problem is that makes absolutely no sense whatsoever. Howe can't move against the Couslands without the consent of the crown. That was never going to come from Cailan, as the Couslands were his most loyal and powerful vassals. Cailan also was a chivalrous sort who had slightly romanticized ideas of what it meant to be a king. There is no possible outcome of a coup against the Couslands where the king doesn't immediately strip Howe of land and title, declare him an outlaw, and dispatch other vassals and troops to seize Highever. Howe needs Cailan dead and someone sympathetic to him in control of the throne for his coup to have any chance of not ending with him dancing at the end of a rope.
Loghain also needs the Couslands dead. He can't have the king's most powerful and loyal vassals hanging around if he's going to betray and murder him. Teyrn Cousland left alive guarantees a civil war, and Redcliffe and Highever both moving against Loghain is going to put him at a disadvantage.
A conspiracy where both the murders of the Couslands and the king were pre-planned just makes much more sense than the alternative. Gaider also didn't seem to realize that the absence of a conspiracy turns two of the game's antagonists into a pair of impulsive nitwits who would have been immediately destroyed by their own stupidity and lack of planning, had it not been for the extraordinary luck of each man's betrayal coinciding with the other's, and conveniently eliminating the person the other most needed dead.