Will the two children become milk siblings, and will the girl become a sister to the questioner, if the questioner's maternal aunt breastfed her younger brother, and the questioner's mother breastfed the aunt's daughter?

"Suckling establishes the same prohibitions that consanguinity establishes. The suckled child becomes a son to the wet nurse and her husband, the owner of the milk. This prohibition is specific to the suckled child himself, not his siblings. So, your brother who was suckled by your maternal aunt became a suckling brother to all of her children. And your maternal aunt's daughter who was suckled by your mother becomes a suckling sister to you and all of your siblings. As for you and your other siblings who were not suckled by your maternal aunt, no prohibitory kinship arises between you and her other children. It is a condition for suckling to establish prohibition that it consists of five satisfying sucklings before the completion of two years of age."