I think I have finally understood the reason why SJ is so evil he is not chani's father I think chani's father died and SJ wife also
Died so they married each other and Chani's mother raised prakash as her own son. Which is why SJ does not mind ruining chani's life because he is not her father which is why a lot widows with children are always scared to remarry because of evil men like him.
I also think she is not his daughter. I have missed several weeks and just watched the last 2 episodes but that is what I am gathering from those epi's as well. Even as a step father he is terrible!