Is it permissible to write a will bequeathing inheritance to only the living spouses and their daughters, to the exclusion of siblings, given that the properties are the product of their own efforts?

A will intended to disinherit some heirs or to harm them is considered a will to an heir, which is forbidden, null, and counts as a grave sin. This is based on the Prophet's (peace and blessings be upon him) saying: "Indeed, Allah has given every rightful person his right, so there is no will for an heir." And because causing harm through a will is forbidden by the explicit text of the Holy Quran, in His (the Almighty's) saying: "after any will has been fulfilled or debt paid, without causing harm." Furthermore, cutting off family ties is not one of the impediments to inheritance. Therefore, the questioner must fear Allah and let matters proceed according to His law.