There is a pretty strong possibility that Yash finds out about this whole debacle through Payal and Palak themselves. Palak could come to Yash feeling all happy and accomplished and boast about how they managed to get Ansh punished by Gayatri (I really wouldn't put it past them at this point). This way Yash would get a version of the story directly from the source, get to know about everything that happened, and will realize for the first time just what kind of upbringing his daughters' are going through! And this might actually become the trigger that forces Yash to sit down and talk to his daughters about everything that is going on, explain Aarti and Ansh's presence in their lives, and to finally encourage them to accept Aarti as their mother. PayPal have yet to hear this all from their father and coming from him, this message might actually hit home! So it's like killing multiple birds with one stone!