OK I don't really get it.wtf is happening with the presidents son? And what's his motivation?.And the 2 sisters r in pain so someone is lying, what is the lies in this chapter?
Not sure where your problems regarding the first two questions lie, I think it was explained quite well over the last chapters.
Rather by "the president's son" do you mean Licht (the original) or Kinou (the one he was copied into)?
His motivation for one is (obviously) revenge for everything the guy had done to everyone, from killing Licht, over the orphans killed to Tomohiro/Xeno and Kinou, however the girls being in pain also shows that the Licht part of him enjoys killing. His denial of this, due to his split personality, was the main lie that hurt them. This is made clear by the older one starting to shake in pain when he states "I'm not like that".