Under custody outside of police station without FIR

Hi Sir, My brother is a private employ working for 12,000/ PM @ Nellore (Andhra Pradesh). One of my brother in law who sold a laptop for 8000/- to my brother and that was stolen one. After that, my brother friends also bought laptops from him. As they are unkown to my brother in law, my brother worked as mediator in this. Recently, the theft person has caught by Police. In the interrogation, he informed that he has sold all the laptops to my brother. On 11th of this month police man took him for interrogation. Till now we are not aware where he was. We have not seen him. As of now, no FIR filed regarding this. only 3 times he called from the police men mobiles with my parents. Requesting you to help us with your suggestions to proceed further. My father was retired Head Constable and one of my brother has joined recently as Constable. They are suspecting, if we take any action against to the Police, in the future my constable bother may face issues. Please help us on this issue. Thanking you sir.