Can My Half Brother From My Mother Claim My Father's Property.

My father had few properties. He had a brain stroke approx 4 years ago but he was mentally stable. He could walk with help of sticks. He did not forget anything. Even he made his signature from left hand epidefit cause his right hand was paralysed. He claimed my brother is not his biological son. Both of my father and brother signed a document where it is written that my brother should make a DNA test in present of my father in order to prove the fatherhood as my father was physically ill. He instructed my brother to arrange all the necessary things and my father was stated in the document that all the expenses would be given by him. My brother did not use to take care of my father. He was very reluctant towards him. But he could not be able to do that DNA verification after 6+ months. My father has expired recently. Now can my brother claim his property. My father was so determined by the fact that my brother is not his biological son. My brother and my mother both used to left somewhere else leaving my ill father alone with me.They used to come very less and denied to take any responsibilities. Now what to do in order to get legally safe. Can my brother has any right to claim my fathers property.