Is it permissible for my father to hide a waqf copy of the Qur’an designated for the mosque in his private chamber to prevent it from being tampered with, especially since there are other copies of the Qur’an available, and would his action be considered a sin because he is preventing others from benefiting from it?

A Muslim is not permitted to monopolize a public endowment to the exclusion of other Muslims, because this violates the condition set by the endower, which scholars have stated is "the condition of the endower is like the text of the Lawgiver, unless it contravenes [the Sharia]." Based on this, your father is not permitted to monopolize the endowment's Qur'an and hide it in the mosque, as this prevents others from benefiting from it.