Indiana  |  Wills and Trusts

I am trying to find out the law on Wills. My mother in law is wanting to make out of a will that her son will be the main executor and he will get a certain percentage and that my wife will get a certain percentage split between the two (i.e. 45%/55%). She wants to stipulate on my wife's share that it will go into a trust account and can only be used for emergency use only. Is that legal and who would decide what an emergency is or not, or can she make that into a will and later my wife can petition for her half or sue her brother for her half.