1. I am an adult. Don't I have any right on my own passport?
Being a citizen of the country your fundamental rights are fully protected by the constitution . You have full rights to obtain and possess an Indian passport if you comply with the requirements to procure it.
2. Is there any way by which I get my passport back from my family?
If the police is not cooperating, you may approach the higher police official with the complaint mentioning that your parents have illegally retained your passport and they refuse to give it back, they do not have any rights to hold your passport, the local police are not taking any action on your complaint to retrieve your passport from them, hence the higher police official is requested to intervene and instruct the local police to inquire and retrieve your passport from your parents and hand it over to you.
Even if this is not working you may approach the judicial magistrate court with an application under section 156(3) cr.p.c. venting out your grievances and seek the magistrate's intervention to direct the concerned police official to retrieve your passport fro your parents and take necessary legal actions against them for illegally retaining your passport.
The above steps if followed, you may get the desired relief.