What is the ruling on a Christian woman breastfeeding an infant, and do her children become siblings to the child?

"Islam is not a condition for fosterage. If a non-Muslim woman breastfeeds a Muslim child five times or more within the first two years of the child's life—meaning the child takes the breast, sucks the milk until it reaches his stomach, and then releases it—then she becomes his foster mother, and her children become his siblings. However, breastfeeding after the first two years of life has no effect."