Preparing a will

Dear Team, I have a query regarding how to execute a will under the following situation. I am 35 and married. I have a sister too who is already married. At the time of my sister's marriage, my father did the partition of all his property and gave me and my sister our share. I got 50 cents with our house and 40 cents were registered in my sister's name. While my father did the partition, he had mentioned that they(father and mother) have the right to stay in the house till their death. But when I applied for a loan, my father had to sign an affidavit doing away with the above mentioned right in the property. Now to the question. I want to ensure my parents' safety in the event of an unfortunate death happening to me while they are alive. Is it legal to prepare a will where in I mention that I want to give unconditional rights to my parents in the above mentioned property(including selling part/whole of it for meeting their day-to-day or treatment expenses) in the event of my death. Also whatever is left after their death should go to my wife and not to my sister. Is this possible to do this. If yes, what is the procedure to do that? Do I need to consult a lawyer in person to do this. If yes, what kind of lawyer? Thanks in advance for your reply. Regards, Arjun Gopal