Sheikh `Abd al-`Azîz b. Bâz
It is permissible for you to be the executor of your mother’s will by selling her house and properties and distributing the collected money according to her wishes. This is part of being kind to your mother. Allah says: “Yet bear them company in this life with justice (and consideration)” [Sûrah Luqmân: 15]
However, I would like to draw your attention to the fact that a Muslim does not inherit from an unbeliever. Usâmah b. Zayd related that the Prophet (peace be upon him) said: “The Muslim does not inherit from the unbeliever and the unbeliever does not inherit from the Muslim.” [Sahîh al-Bukhârî (6383) and Sahîh Muslim (1614)].
However, in this case there is a written will from your mother, so you may receive up to one-third of the estate (33.33%) as a bequest. This is the amount of a person’s estate that he can bequeath to non-inheritors. Since the percentage your mother wishes to give to you and your sons is 40% (20% for you and 20% for your sons), it slightly exceed that percentage. Therefore, you may not receive that excess unless it is approved by all the other inheritors.
And Allah knows best.
Source: Islam Today