You are having a bump in the road to probate. Try to understand why the witnessses have become hostile ? Is it money? Your brother;s influence ? or something else.
In today's world ,technology can help. Their signatures can be verified by comparison of their regular handwriting and signatures on other documents..by a hand writing expert. The age of the paper and age of ink can be determined to close extent by experts.
But all this takes time and money and I don't know if Indian judges even allow such evidence. Ask a lawyer. Try to collect as much circumstantial evidence as possible. People who knew about will, other relevant facts about Wil etc.
If the will is registered..you are in a stronger place.