How is inheritance divided between the mother, the maternal grandmother (mother of the mother), and the two full sisters?

If the heirs are limited to a mother and two full sisters, the mother receives one-sixth and the two full sisters receive two-thirds. The remainder is returned to the mother and the two sisters. There is nothing for the grandmother as she is excluded by the mother. The estate is divided into five shares: the mother receives one share, and each full sister receives two shares. The matter must be brought before the Sharia courts for investigation.