Since the trip from Verbobonc to Rastor took at least two weeks, the party had plenty of time to discuss what they were going to do when they arrived in Rastor. Belaver and Lylamwyn can have any spells prepared they feel like (so Lylamwyn can cast Diguise Self to his heart's content).
I would like to know whether Toriah and Lylamwyn disguised themselves as a particular evil cultist you have met (Chenashi, Festrath, various other cultists) or as a random evil cultist.