What is the ruling on a son marrying his maternal aunt's daughter if her older sister was nursed with his older brother, and what is the ruling on the marriage of the rest of the sons to the daughters in both families, and vice-versa?

It is permissible for a boy to marry his maternal aunt's daughter, unless they both nursed from the same woman. The nursing of her older sister with his older brother does not prevent this. The criterion for prohibition is that it is forbidden for the boy to marry a girl from another family if she nursed five known full sucklings from the same woman he nursed from, or if she is the daughter of a man from whose wives he nursed five known full sucklings.