Try this theory on for size. The cleric of Cayden Cailean is, like all clerics, a psychological outlier. He says funny things like that Asmodeus is his rival, and maybe believes them. The other three start adventuring with the cleric, and he says things like that, and they all learn to play along because they like how he responds if they do or don't like how he responds if they don't.
This is a good theory because it reduces the number of delusional people in the group to just the one.
Actually, now that she's thought of it, it's obviously correct. What a relief.
(Though isn't it a bit odd how realistically they pretend to defer to him in his areas of imagined expertise? If Ileosa squashes this misgiving, it happens too quickly for her to notice.)
Also, implied by the theory is that Lyvina likely disapproves of the way those two are winding the cleric up - the wizard is too kind and earnest for such shenanigans.
It's nice to be predicting things again instead of rolling bewildered with the punches, and Ileosa is going to look at Lyvina's face to confirm that the samsaran is upset.