Hi
Hindu succession Act will be applicable in your case.
The entire stake of your father in law (48%) will be divided equally between the two brothers, surviving mother and your wife.
In the event of you anticipating any foul play, your wife should immediately undertake to do the following
a) Write a letter by Registered post with Acknowledgment due to the Managing Director and also the Company secretary staking her claim in the shares of her father and also submit the death certificate and family member certificate to the company and
b) Also Immediately meet the Registrar of companies in person and submit a written request not to transfer the shares/ make amendments in Registrar of Companies documents without her written consent. Along with the written consent she should submit the death certificate and family member certificate of her father's family.
c) Your wife will also need to apply for succession certificate in the District court where the registered office of the private limited company is located.
Hope this helps.