Is he sinful, who took from the orphans' money deposited with him, being entrusted with delivering it to them monthly, due to his severe need, and is compelled not to give it to them in the following month?

Misappropriating an orphan's wealth for purposes other than their benefit is an act of betrayal and deceit. One must repent and restore the right to its owners. If you are a guardian of orphans and are in need, it is permissible for you to partake from their wealth in a reasonable manner as compensation for your work, as Allah Almighty says: "And whoever is poor, let him partake thereof in a reasonable manner."