Would I have committed a sin if I gave the charity money that my fiancé gave me to my needy family without informing him, knowing that he permitted me to give it to any needy person?

If the suitor did not specify a particular entity or specific individuals for the distribution of charity, and he authorized his fiancée to distribute it with an absolute authorization, then it is permissible for her to give it to her needy family members. However, if the charity is Zakat (definition) al-mal (obligatory charity on wealth), then it is a condition that her family members be among the eight categories deserving of Zakat mentioned in the verse from Surat At-Tawbah (definition): "Indeed, [obligatory] charities are only for the poor and the needy, and those who work on [collecting] them, and those whose hearts are to be reconciled, and for [freeing] captives, and for those in debt, and for the cause of Allah, and for the [stranded] traveler - an obligation [imposed] by Allah. And Allah is Knowing and Wise." If they are not deserving, then she is accountable for the money, and it must be given to those who are deserving. It must be noted that the suitor is a stranger to his fiancée, and it is not permissible to expand on their relationship.