Is it permissible for a male, who was not suckled by the other mother, to marry a girl who was suckled by the other mother once or twice, or not?

There is no objection to one of the brothers marrying the aforementioned girl, as long as there is doubt about the existence of fosterage, or about the number of sucklings that establish prohibition. Nevertheless, it is more cautious to refrain from marrying her due to the suspicion, and to treat her as a stranger. Al-Shafi'i and Ibn Qudamah have clarified that prohibition is not established merely by doubt, because the default assumption is its absence.