What Advocate Kesharwani suggests is like belling the cat. It appears from all that you have narrated that you are not in the good books of your father. If you do not want to disclose the reason I do not want to hear it. You are not worried about the ancestral property. You are only particular about his self-acquired property. As your relationship with your father is not good, he will not bequeath any property in your favour. Are you sure that your father has not already written a Will? It is not necessary that he tells you or even anybody else in the family about his Will. The best thing that can happen to you is that he does not make a Will. If he dies without a Will, you, your sisters and your mother will get equal share. You will be assured of a one-fourth share at least. That may be the reason that your brother-in-law is insisting on your father transferring his property to him during his life-time itself. As I suggested earlier I suggest at least you try to get a caveat saying that your father should not transfer any property to anyone without your prior knowledge. And when you come to know of such transfer, you can try to take preventive action in consultation with your lawyer.
I suspect that you are not disclosing everything. I have many sisters, nephews and nieces. In most cases the nephews are selfish and incapable of making good earnings. On the other hand their sisters and their husbands are considerate. They look after their parents without expecting anything in return. On the other hand, the brothers and their wives have only their eyes on the properties of their parents.
I do not think that your case is like that. Also it is strange that your younger sister is staying with your elder sister and her husband and not with your parents.