The grandfather inheritance cases..
When there are no full brothers or sisters, or parental brothers or sisters, jurists consented that the grandfather takes the place of the father, when the father doesn't exist.
The first case..
His inheritance legally only.
The grandfather deserves the sixth legally only when there's male descendant heir for the deceased.
"وَلأَبَوَيْهِ لِكُلِّ وَاحِدٍ مِّنْهُمَا السُّدُسُ مِمَّا تَرَكَ إِن كَانَ لَهُ وَلَدٌ".
"And for one's parents, to each one of them is a sixth of his estate if he left children."
The second case..
His inheritance by agnation only, the grandfather deserves the remaining of the fortune by agnation, after those who inherit legally, in case there is no descendant heir at all.
"فَإِن لَّمْ يَكُن لَّهُ وَلَدٌ وَوَرِثَهُ أَبَوَاهُ فَلأُمِّهِ الثُّلُثُ"النساء
"But if he had no children and the parents [alone] inherit from him, then for his mother is one third."
The third case..
His legal inheritance and agnation, when there's female descendant heir for the deceased.
"وَلأَبَوَيْهِ لِكُلِّ وَاحِدٍ مِّنْهُمَا السُّدُسُ مِمَّا تَرَكَ إِن كَانَ لَهُ وَلَدٌ"
"And for one's parents, to each one of them is a sixth of his estate if he left children".
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The grandfather inheritance cases with full brothers and sisters or paternal brothers and sisters...
The corrupted grandfather is the maternal father, he doesn't have legal assumptions, he doesn't inherit by agnation, but he is blood relative.
The scholars' sayings about the full grandfather inheritance..
The first saying..
The grandfather is like the father, excludes the full brothers, or parental or maternal brothers, so the full grandfather's cases of inheritance are like the grandfather 's cases; when there are no full brothers or sisters, or parental brothers.
The second saying..
The grandfather doesn't exclude full brothers or parental brothers, they inherit like him with agnation, so that his share isn't less than the sixth..The grandfather excludes the maternal brothers, without dispute.
Benefit...
There are two sayings when there are brothers with the grandfather...
The first..
The sisters take their entitled shares, and the grandfather takes the sixth, or the agnation; what is more.
The second saying..
In the division, the grandfather is considered one of the brothers, he takes the share of two females, and the sister is considered in agnation with him.
For more details refer to
Inheritance science facilitating course / the grandfather inheritance cases.
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The full grandmother inheritance cases..
The full grandmother inherits the sixth if the deceased has no mother.
The mother's mother inherits the sixth if the mother died, the father 's mother also inherits the sixth when the father dies...If both exists (mother's mother, and the father 's mother) then the sixth is divided among them.
The corrupted (untrue) grandmother is the corrupted (untrue) grandfather 's mother..The corrupted (untrue) grandfather is the mother's father.