the definite culprit

I think it is shagun. It's only then the story will move forward. My thought :
If shagun did the accident, she will definitely goes to jail. And Someone has to take care of adi. And it can't be ashok as he is not married to shagun. In that case even if Adi likes it or not he will have to go to his dad..

im thinking adi or shagun

Tumhare Muh mai ghee sakhar. I will be the most happy person to see this track and Adhi realize ishu's goddenss and Raman getting more close to ishu because of that.

Even if Ashok is not married to Shagun. Ashok is the legal dad of Adi. So Adi certainly can stay with Ashok. Ya it is a different matter that Ashok wont be able to take care of Adi.