Are the children of the maternal aunt considered siblings through رضاعة (radha’a - fosterage or wet-nursing), and what rulings result from that, if the aunt placed the children on her chest but no milk was expressed, knowing that they were raised as siblings?

Two conditions are required for fosterage to be a prohibitive factor [for marriage]: first, there must be five or more sucklings; second, it must occur within the first two years of life and before weaning. It is not a condition that the suckling be satiating; rather, merely the act of the child taking the breast and sucking milk is considered a suckling. If no milk is expelled, it is not considered fosterage. If doubt arises concerning the number of sucklings or whether suckling occurred, then no prohibition is established thereby, and the default ruling is permissibility.