How will I know if the WILL of my father is legal or forged

Dear Sir / Madam, My father had 5 children's, both my father and mother were staying with my younger brother from last 25 years Now my younger brother has given the copy of WILL to remaining children's after 8 months since my father died 1. In the WILL he has given 80% to 90% of property to my younger brother who was staying with them. 2. My father's age was more the 90 years when he made this will, by that time he was not able to see properly or remember things because of the age factor 3. The WILL is of 3 pages but the signature of my father is only on last page, even i dont trust witnesses as they are close to my younger brother. 4. He has mentioned all the properties but the valuation of all the properties was not given. 4. He has only mentioned that all the money in bank accounts, FD's and ornaments will be given to my younger brother, but he didnt mention in which banks he had accounts and how many FD's he had. 6. The entire WILL was typed in English, whereas my father cannot read or speak in english. (but i don't know how to prove it) Is there any possibilities of challenging the WILL ??