But if one fears from the bequeather [some] error or sin and corrects that which is between them [i.e., the concerned parties], there is no sin upon him. Indeed, Allāh is Forgiving and Merciful.
Including Parents and Relatives in the Will was later abrogated
This Ayah contains the command to include parents and relatives in the will, which was obligatory, according to the most correct view, before the Ayah about inheritance was revealed. When the Ayah of inheritance was revealed, this Ayah was abrogated, so fixed shares of the inheritance for deserving recipients were legislated by Allah. Therefore, deserving inheritors take their fixed inheritance without the need to be included in the will or to be reminded of the favor of the inherited person. For this reason we see the Hadith narrated in the Sunan and other books that `Amr bin Kharijah said: I heard Allah's Messenger ﷺ saying in a speech:
Literally, al-wasiyyah الوَصِیّہ means an order to do something, either in the lifetime of the maker of wasiyyah or after his death. But, in commonly accepted usage, it refers to what must be done after death. It can be translated as the will or bequest.
Out of the many meanings the word خیر khayr has in Arabic, 'wealth' happens to be one of them, for instance, in the verse وَإِنَّهُ لِحُبِّ الْخَيْرِ لَشَدِيدٌ (Surely he is passionate in his love for good things) where, according to the unanimous agreement of commentators, خیر 'khayr' means 'wealth'.
In early Islam, when shares in inheritance: were not fixed by the Shari'ah, the rule was that a dying person could make a will within the one third of inheritance, leaving behind in the name of his parents and relatives in whatever proportion he chose. This much was their right; the rest went to children. This injunction appears here in this verse.
After someone’s death the problem arises as to how to deal with his or her wealth. The Islamic injunction in this regard is to distribute it in a just and equitable manner to the heirs. One who fears God should follow this injunction regarding the disposal of intestate property in the spirit of justice. This will create a brotherly atmosphere in society, preventing litigation and quarrels over property. Where there is a member of a family, like an orphaned grandson, or any other needy member of the family who does not inherit under the Islamic inheritance scheme, the testator may provide for him, as he has been given the power to dispose of up to one third of his property by making a will in his favour. Islam approves of every lawful device for keeping society free from litigation and quarrels. But unless this is the objective, the changing of the provisions of a will is unlawful.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.