Need protection for my kids from my in laws..

I am a doctor and I hv 3 children of age 7.5 yrs, 5 yrs and 1.5 yrs.The eldest one is a son. My husband and my in laws are all doctors and they run a private hospital. Since marriage I was living with them in my in laws house. They demanded a luxury car and jewels for my marriage .but my father could give only the jewels and not the car as he could not financially afford it. After marriage I was working in their hospital. I then came to know that my father in law and husband has unlawful relationships with the staffs of the hospital. When I questioned I was threatened and asked to leave the house. I then came to my parents house and living with them,hoping that my husband would realize his mistakes and us back.instead they threatened me to sign divorce papers and leave my children under their custody, which would endanger their lives.they have filed a petition again me in the court claiming for the Permanent guardianship of my children. Kindly guide me wht to do next to save my childre