1) If A Muslim youth marries his wife's niece
Legal Effect : The marriage is irregular. The vitiating factor is the bar of unlawful conjunction.
(Irregular marriage : An irregular marriage is one , which falls short of a valid marriage only because of the presence of certain temporary disqualifications peculiar to Mahomedan Law. )
2) If A Muslim marries his wife's widowed stepmother.
Legal Effect : The marriage is void. This is prohibited relationship on ground of affinity.
(Void Marriage : A void marriage is really no marriage at all but mere concubinage. The issues of such a relationship are illegitimate. When there is no contractual capacity or there is no marriage contract or when the parties stand to each other in prohibited degrees of relationships the marriage is void.
3) If A Muslim youth marries his wife's sister.
Legal Effect : The marriage is irregular on the ground of unlawful conjunction.
4) If A Shia woman marries a Christian.
Legal Effect : Among Shias the marriage of a Muslim female with a non-Muslim is void. Among Sunnis such a marriage would be valid as a Christian is a kitabia (i.e. one having a sacred book)
5) If A shia male marries a Brahma Samaj woman for 10 years.
Legal Effect : Brahma Samajists may not be idolators or fire worshippers but they would be non-kitabias for they have no kitab I.e, book by which is meant holy book of revealed religion. Among Shias marriage with a non-kitabia is void. Among Sunnis such a marriage would be only irregular and not a void.
6) If A Shia male marries a Christian woman for 10 years.
Legal Effect : This is a valid Muta marriage for a shia can have a Muta marriage with a non-Muslim kitabia.
7) If A marries B, a woman undergoing iddat at that time. Subsequently A dies. B claims A's property as his wife.
Legal Effect : The marriage is irregular. So there is no reciprocal right or heirship as between husband and wife. B's claim is not tenable.
8) If A , a shia woman, marries a Christian male. Is the marriage valid? Will it make any difference if A is a Sunni woman?
Legal Effect : Among Shias marriage with a non-Muslim is void. If A is a Sunni woman, the marriage would be irregular.