What is munasakha?

Agreed. The second death does not disturb the first estate — it opens a second one on top of it, and the two are solved together. The Kuwaiti Mawsu’a states the rule as that of the jurists at large — “the jurists have held, in general, that munasakha has three states, each with its own ruling” — and footnotes that sentence, at that sentence, to one book of each of the four schools. Reading those four books confirms it. First state: the heirs of the second deceased are the survivors of the first and take from him as they took from the first — typically because they are agnates of both. Here you make a single division and ignore the intervening death altogether. al-Sarakhsi puts the reason bluntly: “there is no point in repeating the division”; al-Nawawi says you treat the second deceased “as though he had never been”; Ibn Qudama and al-Buhuti say “divide the property among those of them who remain and do not look at the first deceased”. So a man leaves five sons and five daughters, and before division a son dies, then a daughter, then another son: the whole estate is simply divided among those still alive, two shares to a male and one to a female. Second state: the people who died after the first do not inherit from one another — brothers, each leaving his own children. Each set takes only its own father’s share. Third state: everything else. Solve the first estate; see what fell to the heir who then died; solve his estate on its own; and if his shares do not divide exactly on his own problem, reduce that problem by the common factor and multiply, or multiply it out in full where there is no common factor. The product is the jami‘a, the combined denominator. A third, fourth or fifth death before division is handled by repeating the same step against the running total, and the arithmetical check is the same in all four schools: add up the awards, and if they do not come to the combined denominator, do it again. We checked this point; the schools do not differ on it.

Shared evidence: al-Mawsu’a al-Fiqhiyya, “Munasakha” §§1–3 — “dhahaba al-fuqaha’u fi’l-jumlati ila anna li’l-munasakhati ahwalan thalathatan li-kullin minha hukmuhu”, footnoted at that sentence to Radd al-Muhtar (Hanafi), al-Qawanin al-Fiqhiyya (Maliki), Tuhfat al-Muhtaj and Mughni al-Muhtaj (Shafi’i) and Kashshaf al-Qina’ (Hanbali) · Hanafi — al-Sarakhsi, al-Mabsut, Bab al-Munasakha: where the second deceased’s heirs are the first’s and the division is unchanged, “fa-innahu yuqsamu qismatan wahidatan; li-annahu la fa’idata fi takrari al-qisma” · Maliki — al-Dardir with al-Dasuqi, [al-Munasakha]: the term is used by the specialists “fi’l-faridati allati fiha mayyitani fa-akthar wahidun ba‘da wahidin qabla qasmi tarikati al-awwal”, in three sections, the first of which “needs no working” because the second’s heirs are the remainder of the first’s · Shafi’i — al-Nawawi, Rawdat al-Talibin, al-nazar al-thani fi’l-munasakhat: two states — “fa-taj‘alu al-mayyita al-thaniya ka-an lam yakun wa taqsimu al-tarikata ‘ala al-baqin”, or else “nusahhihu mas’alatay al-awwali wa’l-thani jami‘an wa nanzuru fi nasibi al-thani min mas’alati al-awwal” · Hanbali — Ibn Qudama, al-Mughni, mas’ala 4851: “ma‘naha an yamuta min warathati al-mayyiti insanun qabla qasmi tarikati al-awwal”; and al-Buhuti, Kashshaf al-Qina’, Bab al-Munasakhat: “wa laha thalathatu ahwal” · Hanbali, and the arithmetical check both Hanbali books give — al-Mawsu’a §§5–7, on a third, fourth and fifth death before division: “wa’l-ikhtibaru bi-jam‘i al-ansiba’i fa-in sawa hasiluha al-jami‘ata fa’l-‘amalu sahihun wa illa fa-a‘idhu”.

Not covered by this finding: Munasakha is a method for combining two divisions. It does not settle — and cannot settle — two things it sits on top of. (1) The underlying faraid sums. If the schools differ about the shares in either estate, they will differ about the answer while applying the identical method; the classic instance is a grandfather inheriting alongside brothers, where the Hanafi and majority positions diverge and the munasakha is then “corrected” on two different footings. (2) Whether the shares had vested at all. Where the first deceased left debts, the Hanafis and Malikis hold that ownership of the estate does not pass to the heirs until the debt is paid, while the sound Shafi’i view and one Hanbali narration have it pass before payment — which is a live question precisely when an heir dies before division. Nor does this entry address deaths that were simultaneous: al-Dasuqi expressly takes those out of munasakha, and they are a separate question with a real four-school split. — not yet researched school by school. Treat that as open and ask a scholar of your school.