Oh, there are quite few quotes throughout this passage that could suggest Istryia is a skin-spy. The bottled up of her quote. Also, her seeming so out of the loop. You can tell she is clearly begging Xerius to go along with Maithenet, in hindsight, what the Consult wants. They only know that all their SS's are being outed by the Cish. Fairly strong case for SS Istryia.
Not Skeaos though. I think he is replaced to sway Xerius. Probably at the orders of SS Istryia, to have a common peer among the Nansur.
In hindsight, that Mallahet is Moe is a smack to the face. We see that he is feared and has powers other Cish dont possess.
Again, Xerius is such a tragic character. ToT really spelled out all his weaknesses. But, if not for a lone Dunyain, Xerius plan most likely comes to fruition. So I can't call him a total fool. You just get the feeling reading this chapter, he'll be the 1st big charactwr to fall.