Am I allowed to take the charity money given to me with the intention of giving it to a poor family, and use it to pay off my debts, knowing that the donor has authorized me to dispose of it freely, and that I am in debt and my salary barely covers the necessary living expenses?

It is permissible for an agent distributing sadaqat (charitable donations) to take from it for himself to settle his debts. This is the view of the Malikis and preferred by some scholars. However, it is more cautious to abstain from doing so, to avoid disagreement. This is provided that the principal has given the agent freedom to dispose of the money in its distribution. But if the principal specified a particular recipient or a specific person, then the agent is not allowed to overstep that.