What is the overview of this specified system of inheritance distribution?

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A surviving husband’s share is either ¼ or ½, depending on if they have children.
If they have children, a surviving wife’s share is either ⅛ or ¼.
Other shares are ⅙ for the father, and ⅙ for the mother.
The rest goes to the children, with two shares for the son for every share for the daughter.
If the children are only girls, and the deceased has no father, it may be possible that the brothers of the deceased may inherit.