What is the ruling of Islamic law concerning a man who married a woman, then married her sister's daughter while both are still his wives, and what is the ruling on the inheritance of the children from both wives, and what is Imam Malik's madhhab on this?

It is permissible for a man to marry the paternal aunt (ʿammah) of his deceased or irrevocably divorced wife, or of his revocably divorced wife after her waiting period (ʿiddah) has ended. The same applies to marrying her sister. However, combining a woman with her paternal aunt or her maternal aunt (khālah) in marriage is forbidden (ḥarām). If they are intentionally combined, the marriage of the second wife is annulled, and the marriage of the first wife remains valid if it preceded the second. The children of each wife inherit from her and do not inherit from the second wife. The man inherits from his children, and they inherit from him in both cases. In the case of an invalid marriage (nikāḥ fāsid), the child is attributed to him, and inheritance follows from that.