father not coming to take his wife and child

My sister came to delivery and gave birth to a boy. Her husband has not come to see the baby nor to take them home. They are at mom house since 8years. Parents went to his house to talk but he is not there, he has a elder brother who send parents out saying they don’t know where he is. Till now we don’t know where he is. We have tried so much to talk to them and once we went to police but they didn’t solve the case. They called him to station and send him without intimating us, they bribed police and escaped. We don’t know how to proceed with cases, what can we do? How can we get the child his rights? Please help us, they are very clever and have influences, they deceived my sister and our family