Six months as the least duration for pregnancy

Q: I am an Indian Muslim. I married an Indian girl who was a Hindu. As I learned a lot from the teachings and debates of the remarkable scholar Sheikh Ahmad Didat about methods of Da`wah, so I called her to Islam and she accepted. I married her fifteen days after her embracing Islam. I knew that she was thrown out from her family's house before I married her. She told me that her family did that because of her conversion. I married her in 25/3/1989, and I discovered that she is not a virgin. She argued that this happen during her playing sports, especially horseback riding. On my part, I forgave all that has happened in her past. The pregnancy tests showed that she is going to give birth on 4/10/1989, a matter that aroused suspicions among my family due to the unexpected time of giving birth. They treated her so badly, especially my step mother. They even deprived her from eating with them and then she was thrown out of the house. I took her to live in a room that is 1000 km away from our district. She gave birth on 17/10/1989 i.e. after six months and half or nine weeks from her pregnancy. My family refused to admit this child and his mother regardless of any possible excuses or reasons. She says that the baby is mine. I took her to six Hindu doctors including a friend of mine, to examine her. (Part No. 19; Page No. 10) They all agreed that the baby was born after nine months, for if it was born after six months and half, it would have required placing him in the incubator for a month and not just three days as was the case. My family is pushing me hard to divorce her but I do not know what to do. Is this baby really my son? My wife has no one else but me. If I leave her, she may return to the false creed again and leave Islam. Moreover, the baby would not be raised according to the Islamic principles. What should I do to keep the mother and the baby attached to Islam? Kindly, give me your Fatwa in this regard.