Should the money that was handed over with the intention of giving it as charity be given to the giver's wife to spend on the needy children, or should it be given as charity as requested by the giver, knowing that his sister (who was specified to receive a portion of the money) cannot be consulted for her opinion?

If the woman is aware of her actions, then her authorization for someone else to give charity on her behalf is valid, and the agent is bound to act according to the authorization. However, if she is not aware, then it is not permissible to donate her money as charity, because it is part of the assets of a legally incompetent person. It is permissible to give charity to her needy children without informing her.