Executor not following the will

My father registered a will under pressure from my brother and sisters in which it was mentioned as follows -1) His estates were defined and the distribution ratios of his 4 children defined. 2) Executor - my sister was to get the possession and sell the state. First preference was given to my brother to buy the property at highest market price. and the proceeds to be distributed as per the will after paying of the liabilities. One of the liability mentioned was to my brother, which my brother claimed had given to my father and most of it was the payments made to vendors, etc in their joint business, with a quarterly compounded interest @ 15%. These claimed liabilities were from the year 1990 until 2014. 3) My father was harassed continuously by my brother and his wife and hence he finally had started legal proceedings to get my brother and his family to vacate the house. There were legal notices exchanged between their respective lawyers. In these notices, my father clearly claimed that he didnt know any money to my brother and the claim was bogus. 3) The executor executed the sale deed in favour of my brother for 1.3 Cr for a property of market value between 7-8 cr, the day after I left for USA for my daughter's wedding. I had no intimation and I feel they are trying to take over all properties and assets of my father without any fair distribution as per the will. Some questions - 1) Can I challenge the will? 2) Can I challenge my brother's claim of my father owing money to him 3) Can I initiate some criminal proceeding for fraud? 4) Can sue my brother and my sister (executor) PLEASE DO GUIDE AT THE EARLEIST.