Is a young man breastfed by the mother when she was single and a virgin, and had no milk, considered her son, thereby prohibiting him from marrying her sister?

Suckling establishes the same prohibitions as lineage, for the Prophet, peace and blessings be upon him, said: "What is prohibited by lineage is prohibited by suckling." The suckling that establishes prohibition consists of five full, satisfying sucklings. If the mother did not suckle the aforementioned young man, there is no harm in him marrying her daughter. What the mother feels as discomfort is merely a form of intrusive thoughts (waswasa).