Father has two wives and has inherited property

My grandfather passed away in 1992 and made will on my father of all his property which he himself has inherited. My father two wives and both the marriages are arranged. Each has two sons all are major and married. I am the son of second wife. Both wives do not have a marriage certificates (according to my knowledge) and have ration cards individually mentioning my father's name in it and living in the residential address as two families.Hence, have some other proofs like Voter id, aadhar and account in National bank mentioning those addresses. My father is alive and does not have good terms with my mother but staying in same house. 1. In case if my father gives any property to one wife and sons, say to the first wife or any of her sons, is it correct legally? 2. Can my father write a will in favour of any one family ? Guess he can write will of what he himself has earned in his lifetime. But will on the property that he himself has inherited be legal? 3. Should I get marriage certificate for my mother ?Would she get equal rights as the first wife? 4. Major thing : During my marriage registration, my brother got signature from me and from my wife on a blank paper 5 years back. As the terms are ok until recent past I did not mind about it but now has a doubt. What action should I take so that the blank paper signature will not put me in trouble. Asking him directly won't work and also it will worse the situation. Hope you understand.