What is the ruling on marrying the daughter of the wife's sister's son, and does the ruling on combining a woman and her maternal aunt apply to her?

It is not permissible to combine a woman with her sister's daughter's daughter or her sister's daughter's daughter. Similarly, combining a woman with her father's or mother's maternal aunt, or her father's or mother's paternal aunt, is like combining a woman with her paternal aunt and maternal aunt. This is forbidden by the consensus of the Muslim imams, and the marriage to the second woman is null and void, not requiring a divorce.