Marrying a paternal uncle's ex-wife
Is it permissible to marry a paternal uncle's ex-wife, taking into account that the mother of the person who wants to marry was previously married to this uncle, and that this uncle had fathered children from both women?
A paternal uncle's wife is not from among those who become unmarriageable due to lineage or nursing. The seven categories of women to whom one is prohibited to marry due to lineage are mentioned in Surat an-Nisaa`. Allah says,
Prohibited to you [for marriage] are your mothers, your daughters, your sisters, your father's sisters, your mother's sisters, your brother's daughters, your sister's daughters, your [milk] mothers who nursed you, your sisters through nursing, your wives' mothers, and your step-daughters under your guardianship [born] of your wives unto whom you have gone in. But if you have not gone in unto them, there is no sin upon you. And [also prohibited are] the wives of your sons who are from your [own] loins, and that you take [in marriage] two sisters simultaneously, except for what has already occurred. Indeed, Allah is ever Forgiving and Merciful. [Al-Nisaa`, 23]
In addition to the above the prohibition extends to step-mothers and any other woman who becomes unmarriageable through nursing. Hence, an uncle's wife is not from among the women prohibited in marriage. There is no harm if the mother of this person who wants to marry his uncle's second ex-wife, was previously married to his uncle.
It is permissible for the inquirer to marry his uncle's ex-wife as long as there is no other obstacle to the marriage such as nursing relations, or any other such reason.
Allah Almighty knows best.