Is Shaimaa—who was nursed with the questioner by the same mother—considered his sister through rada'a (nursing), and are her parents considered his parents?

If the suckling (radha'a) is proven, then Al-Shaymaa would be your sister by suckling, and the nursing woman, Fatima, would be your mother by suckling, and her husband, the owner of the milk, would be your father. So, if an infant drinks the milk of a woman, he becomes her child and the child of her husband, the owner of the milk, by estimation.

According to the Maliki school of thought, the testimony of a single woman regarding suckling is not sufficient, even if she is trustworthy. Suckling is proven by the testimony of two trustworthy men, or by the testimony of one man and one woman, or by two women if the matter was widely known (fasha al-amr) before the marriage contract. If it was not widely known before the contract, it is not proven. Widespread knowledge is not a condition if the witness is a man with two women.

The testimony of one man and one woman, or two women, or two men, must be from individuals other than the parents of the spouses. There is hesitation as to whether trustworthiness is required along with widespread knowledge. Suckling is not proven by the testimony of a single woman, even if she is trustworthy and the matter was widely known.

It is recommended to be cautious (al-tanazzuh) in every testimony that does not necessitate separation, such as the testimony of a single woman, or a single man, or two women where the matter was not widely known with them. Caution means not marrying her if she is not already a wife, or divorcing her if she is a wife.