Female child custody

CHILD CUSTODY Sir, 2 months back my sister's daughter in law suicide by hanging and written final statement nobody response for her final decision. at Pollachi..Postmortem reports shows clearly only suicide. Female Childes ( Age 4) mother side grand parents taken her to their native place Trichi. and refusing to return back the child to her father ( My sister's son ) My sister side approached through Police to get back the child. But child's mother side grant parents refused to hand over the child, and with the help of local MLA replied to get the child through court. So to the above situation we don't know how to get back the child immediately because her school education is spoiling. Hence requesting you to inform me what are the steps i have to take immediatly to get back the child. Expecting yours kind consideration in this regard. Thanking You, Regards,