1. the house constructed by you on the land of your grandfather will be considered as the property of your grandfather.
2. If your Uncle can manage to get the gift deed or will registered/executed in his favour or in favour of his wife, he or she will be able to claim title of the said property.
3. However, if your grandfather executes a will in favour of your Uncle or Aunt, he/she shall have to file an application praying for grant of probate and in that case all the legal heirs of your grandfather including your father will get the chance to contest the said application for grant of probate.
4. The police complaint and the medical prescription as suggested in my earlier post will be of great use while challenging the validity of the said will.