Dear Ajay
My opinion on your queries are as under:
What are the strength of the Purchaser or bank ? Why would purchaser still going ahead with construction without fear? If he loses the case then can he claim that he had invested so much money in the construction and also mortgage the X property for same ?
Opinion: he may claim his money from your father who mortgage the property or sell the property to him, purchaser may file a civil suit for damage against your father and also file a cheating case.
2) Suppose if i win the case then is it possible that my father would get Life interest in the property again? what measures should be taken to make sure that he should not get Life interest as he has misused my grand mothers Will.
Opinion: as per Will he will be the interested in the property and entitle to use the same but can not sell the property, no law of india can restrain him to enjoyed the property.
Is there any law or case examples that mis using of will will result in loosing the rights of the property.
Opinion: what is the misuse of Will, as per your information the will she mentioned that the property x can be enjoyed by father as life estate and vested reminder to you. Then he has all rights to use the property, let out the property, mortgage the property, construct the property but your interest can not be denied, after him this property will goes to you, hence the property can not be sell by any means by him or any body till he alive.
Feel free to call