Is it permissible for Munir to marry Karima if Ahmed and Fatima were nursed together, given that Munir is Ahmed's brother and Karima is Fatima's daughter?

There is no legal impediment for the aforementioned brother to marry the aforementioned girl. Consanguinity (due to nursing) occurs when they both suckle from the breast of the same woman, whether she is the mother of one of them or another woman. If they did not both suckle from the breast of the same woman, and she is not his niece or sister through nursing, then there is no objection to the marriage.