Is it permissible for Khalid to marry Fatimah, the daughter of his sister's brother through rada'ah (nursing)?

Nadia's brother is your foster brother, and it is not a condition that you have nursed with him. If the legal fosterage occurs (five breastfeeds during the weaning period), then all children of the foster mother become siblings to the one she nursed, whether they nursed with him, before him, or after him. Therefore, the daughter of Nadia's full brother is the daughter of your foster brother, and it is impermissible for you to marry her because you are her paternal uncle.