By compromising the brother, they also compromise the sister. She's relying on the brother to learn what's going on, after all. If he gets distracted, she won't get all the information as accurately and as quickly as she needs to.
Hmm already forgot what these succubus can do ( maybe I should go back and check).. But I hope its some magic that makes him horny as fuck.. So horny all he can think about is jacking off.... or
shoving his smol pp in his sisters mouth. I'd find that fairly amusing
I am actually curious how the strong is this Pheonix girl, but at least her bodyguard seems strong.