Wife and parent-in-laws keeping me away from my child

My marriage - 4 years old. Wife's status - Has gone for delivery 3 years ago to her parent's house (They forced us to bring her in as they say it is a custom although we did not prefer to make her travel in her 6 mth of pregnancy). Delivered a boy, and for last 2 years have been making excuses but not returning back to home. Parent-in laws never phone and avoid discussion on sending her back and child. My status - During delivery, I was with them and asked them I should cover all expense. They refused. They were to return in 3 months, but when they did not I went again on my child's 1st birthday. They taunted that they are having financial trouble. I gave them 1 lakh cheque. Even then wife never returned. On my child's 2nd birthday when I went, they now demand 5 lakhs for medical treatment. I just demanded medical bills so I can put them in my Rs. 15000 tax benefit claim. They made so much hue and cry over this, but did not gave me Medical bills. They keep on demanding money through my wife, but on my face my In-laws say we don't need any financial help. 1. I want my child back and want to know what legal edge (success rate) I have ? 2. What tips should I know / do - to make my case stronger of child custody (knowing that laws are highly biased towards mothers).