Is it permissible to pay off the debt of a legal guardian from the Zakat funds of the orphans under his care, given that his monthly salary makes him independent of Zakat?

First: Zakat is obligatory on the wealth of orphans and others if it reaches the nisab (minimum threshold) and a hawl (full lunar year) passes over it. It is recommended for the guardian of an orphan to invest the orphan's money so that zakat does not deplete it, based on the saying of Umar ibn al-Khattab: "Invest the wealth of orphans so that zakat does not consume it."

Second: Whoever is entrusted with distributing the zakat of another is not permitted to take from it for himself, even if he is deserving, unless he has the permission of the owner of the wealth. Therefore, if you are the guardian of orphans and the trustee of their wealth, you are not permitted to take from their zakat for yourself, due to the lack of permission from the minor and the strong suspicion involved in such a case.