what are the rights of child born out of extramarital affair

My father is 60 yr old married to my mother 31years back(Arrange Marriage). After 6 months she came to know that my father is having extramarital affair with another women and my father married to that women also, but i dont know after or before marrying with my mother. My father used to go to meet her 3-4 times a year but from last 4-5years my father is not going to meet her because that woman don't like my father anymore as my father become old, weak and ugly. That women is having Central Government job and having a good financial condition compared to us we are having poor financial condition, burden of loans i hv completed my education on loan and paying it off through my salary and helping my sister too for her further studies. Now, my father has a 18year old son through that women who is calling my father and demanding for 2-3 lakh cash for admission in college and threating my father that if my father won't pay cash to him then he will sue my father in court for not giving financial support in education. We are not in a condition to pay even ₹10k. Now what action can be taken against them for their act of having involved with my family, putting the life of my family under torture. My family is on the verge of destruction. What action can be initiated against them, what are the right of that Extramarital affair child and weather he can sue on my father or not. Please help. there is lot more to write, but it is too painful to put on everything right now. Kindly suggest some solution.---regards