Do I have to give my child back to the grandparents?

The grandparents on the mother’s side have "temporary custody" signed only by the mother. The won't show me any documentation of anything, but It's not signed by a judge. There were no prior legal custody arrangements before this. It was written up by their lawyer. I, the father, still have my half of the custody. My name is on the birth certificate. They have been withholding my daughter from me for almost two months, trying to use her as leverage to get me to sign my rights over to them. They were trying to coerce me into signing over saying I can't see her until I sign my rights over to them. I think maybe their lawyer advised them to let me see her, or else they wouldn't have decided to let me take her for the night. They are saying they would call the police if I didn't return her. Do I have to return her? They don't have anything from a judge stating that that is where she has to be or that they have full legal rights. I was told to call their bluff and tell them I want proof of documentation signed by a judge stating that they have the legal right to make the decision on if she has to stay there or not. I mean, nothing has gone to court. They have been saying for almost two months that I was going to be served court summons but have received absolutely nothing. But I don't want to call their bluff only to find out I do actually have to return her over there, then they don't let me see her again.