No topic in Islamic inheritance is as debated by lawyers, attorneys, and orientalists as Grandchildren's share. Muslim grandchildren inherit as primary heirs in the absence of children. The Grandsons inherit in the absence of the Sons. The Great Grandsons inherit in the absence of Sons and Grandsons.
The Grand Daughters inherit in the absence of the Daughters. The Great Grand Daughters inherit in the absence of Multiple Daughters and Multiple Granddaughters. However, the descriptions under Islamic law regarding Grandsons and Granddaughters differ largely regarding eligibility.
The Grandsons receive shares are Sons of Sons in the absence of Sons, and it continues on descendants in the same pattern. In other words, Granddaughters cease their rights as fixed sharers and convert into residuary. In the absence of Grandson, the Granddaughter's share can vary in certain conditions due to the decrease or increase of total shares under the Radd and Awal (or Aul) scenario.
The Granddaughters receive shares are Daughters of Sons if no Sons and no Multiple daughters survive, and it continues on descendants in the same pattern. Refer to this Grandchildren Inheritance chart to see the picture more clearly.
There are certain Hajb (i.e., exclusion) rules that are applicable to Grandchildren. Sons of Sons and Daughters of Sons inherit when Sons do not survive. Children of Daughters do not inherit but can get a share as a distant kindred (subject of Madhab's differences of opinions).
Multiple daughters block or exclude Daughters of Sons. Grandchildren inherit fixed and residuary shares similar to Children. Granddaughter inherits 1/2 (i.e., one-half) if single and 2/3 (i.e., two-thirds) if multiple. Granddaughter inherits 1/6 (i.e. one-sixth) if single when surviving with a single Daughter. Grandsons receive independent and joint residue similar to Sons.