The two ‘Umariyyatan cases

Agreed. In the two configurations husband + mother + father and wife + mother + father, the spouse takes his or her Qur’anic fraction first (a half, or a quarter), the mother then takes a third of what is left rather than a third of the whole estate, and the father takes the remainder. So with a husband the split is 1/2 : 1/6 : 2/6, and with a wife it is 1/4 : 1/4 : 1/2. Ibn Qudama reports the ruling as ‘Umar’s, followed by ‘Uthman, Zayd ibn Thabit and Ibn Mas‘ud, and then names Malik, al-Shafi’i and the Hanafis as holding it — on a text of al-Khiraqi that states the Hanbali position itself. That is all four schools in one passage. The reasoning is that where the parents inherit together the father takes twice the mother, and that proportion should survive the spouse’s share being taken out first. Ibn ‘Abbas held the mother should take a third of the whole; Ibn Qudama concedes his argument from the bare wording of the verse is a strong one, and says only that the Companions’ consensus had already closed against it. We checked this point; the schools do not differ on it.

Shared evidence: Surah an-Nisa 4:11 — “if he is childless and his parents are his heirs, his mother receives one third” · Surah an-Nisa 4:12 — the spouse’s half and quarter, which are taken out first.

Not covered by this finding: the same configuration where a grandfather stands in the father’s place — on the Hanbali rule stated in al-Mughni the mother then takes a third of the whole, which is not the ‘Umariyyatan result, and the other schools’ treatment of that variant — not yet researched school by school. Treat that as open and ask a scholar of your school.