Are the foster brothers and sisters mentioned in the question considered mahrams to each other, as well as to the rest of the relatives?

If a child is nursed five times, and this occurs before the age of two years, then its legal rulings take effect. Your maternal uncle, who was nursed by your mother, is your maternal uncle by lineage and your brother by suckling from two sides: your mother and your grandmother. He is also a maternal uncle to your siblings and their brother by suckling. Your maternal aunts are your sisters by suckling. The sons of your maternal aunts are not mahram (definition) to your sisters. You are mahram to the daughters of your maternal aunts and uncles. Your maternal uncle, who was nursed by your mother, is the only mahram to your paternal aunts.