What is the ruling concerning the determination of inheritance shares when two Muslim sons disagree on the timing of their father's conversion just before death?

Primary text

Inheritance is given only to the son who is agreed upon as having been a Muslim at the time of the father's death. The disputing brother must take an oath denying the knowledge of his brother's conversion before the division of inheritance, as the default state is disbelief until proven otherwise. However, if it is established that the son converted before the division of the estate, he is entitled to his share.