Will can be made on a simple plain paper, it should be signed by the testator and 2 attesting witnesses. Though it is not mandatory to register a will but still it is advisable to register it.
Registration of will is optional but if you register then it will more helpful in case of proving it.Registration is done through registrar office.
first you simply draft it ,if you don't know how to draft you download example form on this site and make your own will and register if you are doing so.If not register then it witnessed by two witnesses.
Go to www.vakilno1.com/wills/Types-of-Wills.php
Download the form .
I agree fully with M/s Advocate Archana and Kushan Vyas.
For your next point:
Kindly get the legal heir certificate from local Tashildar where your father-in-law was residing and apply for succession certificate for the legal heirs of deceased in respect of moveable and immoveable properties left behind by the deceased. in proper civil court.
As regards your present problem, since the person has expired without making a Will, the only option is to apply for Succession Certificate from a Court of Competent Jurisdiction as regards his movable properties which includes Fixed Deposits, Money in Bank Accounts, Posta Offfice Savings, Shares and Debentures, Car etc.
For immovable properties such as land, building, flats, offices etc. no succession certificate is required as the legal heirs entitled to inherit automatically becomes the owners of such property in accordance with their right of inheritence.
For future, if any living person wants to make a Will, it can be made on a plain paper, no stamp paper is required, and the Will need not be registered. Two Witnesses are required to sign the Will as Witnesses. However what is important is that the intention of the testater (person making the Will) should be very clear and unambiguous and should be esily capabkle of being understood. So therefore one can make the Will oneself, it is always better to take the help of a legal professional so that the Will is drafted in an unambiguous manner and all the properties owned by the testater is included in the Will