Heirs were appointed by the Shariah i.e. the near relatives of the deceased who become his or her heir after death. No one can make any one as heir from his side. However, if one wants to give some part of property to someone who is not his heir then he can give him in his lifetime by giving it into his possession or making a will to give him from his one third property. The first one shall be called as hibah (gift) while the second one will be wasiyyah (will). A man can do hibah and make a will out of his one third properties with the condition that he does not have intention to deprive the legal heirs or to harm them.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband