Is it permissible, Islamically, to divide the recitation of the 60 Hizbs of the Quran among several individuals, so that each person recites their portion in a low voice? And was such an act ever authentically reported from the Messenger of Allah, peace and blessings be upon him?

Reciting the Quran is among the best deeds, especially in Ramadan. For the reciter of a single letter, there are ten good deeds, and it will intercede for him on the Day of Judgment. The Salaf (pious predecessors) used to devote themselves to reciting the Quran in Ramadan, with some completing it daily or every two days. However, it was not reported that they gathered to recite it in the manner described; rather, each individual would recite for himself, and one's recitation does not benefit another. It is not accurate to claim that you have completed the Quran since each person did not recite it in its entirety. There is no harm in a teacher encouraging his students to recite the Quran, each according to his ability, on any given day.