Please turn to the Qur'an for guidance. Read every word in 2:180-182.
2:180 Regarding proper dispensation of property, it is prescribed for you, before death approaches any of you, and he is leaving behind much wealth, that he set up a will for parents and family in a decent, equitable manner. This is a binding duty on the upright.
[Any oversight or leftover from the will shall be distributed according to portions Divinely assigned in 4:11-12. Please remember that most Muslims forget this point, and some ‘authorities’ even revoke 2:180! How can a father will to impart equal portions to two of his sons when one of them might be righteous and needy, and the other one wicked and prodigal? ‘When death approaches any of you’ carries the reminder that it is always close and unpredictable. At the same time, it takes into account the final assets of a person]
2:181 If anyone tampers with a will after hearing it, the guilt befalls those responsible for altering it. Certainly, God is Hearer, Knower. [A will shall be attested by two trustworthy witnesses. 5:106]
2:182 (The one who makes a will, the testator, is likely to make errors.) So, if anyone, who has heard the will, fears some bias or diminishing of a due right, and then makes a mutually acceptable correction between the concerned parties, he will not be harming himself. Indeed, God is Absolver of imperfections, Source of all beneficence. [Ithm = A violation that drags down human potential or harms the ‘self’]