Is succession certificate valid to claim a share in property

Dear Concerned , My brother had died in this year and he had kept nominee to my mother at place of his wife as he has not not any faith on his wife.However now my sister in law has filed a succession certificate for herself. Please respond for the following questions 1. Effect of succession law 2. My mother does not need that money however she wants to secure future of her grandchildren so that all the money can not be spent by my sister in law.We have doubt that after getting money she will leave children . Please suggest path.Does the concept of trust applicable in this case . Can we ask court to create on trust for my brother's money so that earning/interest on money can be used for children and they can get principle amount after attaining the age of 21 yrs.