The Kishnar sisters had no business asking the First Prince how it was sentient of their names. As far as they're concerned, the monster of an opponent that they had was already an enigma. For all they knew, Avarhatus could be capable of taking down a realm or two.
Well, their queries would all be answered if they were aware of Avarhatus' identity. But nothing would change if they did. The perilousness of their circumstances, no matter how extensive their knowledge about the First Prince was, wouldn't change. In the first place, they had already assumed that the demon could read their minds, yet they did nothing to counter it.
Striving to conceal their thoughts would only serve as another burden for them. Hence, rather than trying to hide their plans, they sought to enact them even if Avarhatus was aware.
"It seems that I have to get rid of the two of you. I'll give you credit for being persistent, thus annoying me in the process."