tell me if the nikah of the son is broken if his father sleeps with his son’s wife? Also if the son’s wife is his mother’s niece then what about his father’s nikah with his mother?

Incest, in whatever form, is a very grave and detrimental sin in the viewpoint of the Shari'ah. Not only does this heinous act result in great punishment in the hereafter, but in the very world it sets off a frightening chain reaction. Consider the following Shar'ee ruling:

Should a man commit adultery or even touch a blood relative with lust and desire then automatically the Usool - ascendants (parents, etc.) and Furooh - descendants (children, etc.) of both parties become Haraam (forbidden in marriage) upon each other. (Shaami Vol. 2 pp. 32-36).

Example 1: If a man touches his daughter-in-law with lust and desire then his son and daughter-in-law (son's wife) become Haraam upon one another. They can no longer stay together with one another as husband and wife.

Example 2: If the father touches his daughter with lust and desire then he and his wife (his daughter's mother) become Haraam upon one another.

THE MUSLIM PUBLIC IS HEREBY NOTIFIED THAT THE DARUL IFTA IS FREQUENTLY FACED WITH THE ABOVE SITUATIONS AND THE CONSEQUENCES LEAD TO MARRIAGE BREAK-DOWN AND UNTOLD HEARTACHE.

In order to avoid the ghastly consequences of the above types of situations, it is advisable that men and women strictly adhere to maintaining the Laws of Purdah and separation of sexes, which have been prescribed for the peace and harmony of mankind.

If the son's wife is his mother's niece, then the father's Nikah still remains intact.

and Allah Ta'ala Knows Best

Mufti Ebrahim Desai