This is something meant for Islamic estate planning: the doctrine of Al-Awl, where the total sum of the fractional distribution of a Muslim deceased’s assets to the heirs, according to the Faraid, does not add up to one. The Doctrine of Al-Awl then applies, where all the shares are decreased proportionately.
Although I had undergone a training on Islamic Estate Planning many years ago from as-Salihin Trustees Berhad, I have to base this post on explanation obtained from an on-line forum. You can read it here too.
As an example, if the distribution of property is among a husband, mother, daughter and son’s daughter, their shares will be: Husband 1/4, Mother 1/6, Daughter 1/2, Son’s daughter 1/6. Total Shares = 13/12. Since the share distribution is more than what’s available, the Doctrine of Al-Awl shall apply.
Al-Awl only occurs when there are improper fractions. Typically, improper fraction only occurs when the denominator is 6, 12, or 24.