It seems your wife is living in a bad environment, as is your son. Not definitely healthy for your son. Unfortunately the courts can not do anything more than providing you some visitation rights here.
You look like a very good person with love for your child. For the sake of love towards your son, did you try to reconcile your marriage in any way ? It is easier to change your wife's attitude and create interest in her own marital family once she starts living with you. She needs to understand the value of a healthy family and the importance of a responsible father in the family.
When did you get separated ? There are millions of families out there where both parents love their children but not each other and live their lives somehow. As time progress, lot of issues can be sorted out and children influence a lot in the family matters.
You mentioned your wife is trying for divorce. If so, use that opportunity to go to the mediation cell and show your interest to save your marriage for the sake of your son. Who knows, with all the counselling she might change. Also once she comes home, she might change good for the sake of son. Never ever show your irritation or get upset with her action just for the sake of your son.
Alternatively you can file for Restitution of Conjugal Rights S.9 of HMA and request her to come and join you. It may be initially hard, but if things can be worked through mediators and counsellors it will work good. I am not from Hyderabad, so I do not know directly any advocate. Someone from this forum might be able to suggest you a good advocate.