Is the giver of charity obligated to inform the poor that the money is from someone else? And is their failure to inform them and give thanks to him considered to be among those "who love to be praised for what they have not done"?

It is permissible for the agent to give charity from the money to his poor relatives if the owner of the money grants him permission to do so. There is no harm for the agent to give his brother from this charity, as long as he does not intend personal gain or praise by it, as stated in the Almighty's saying: "We feed you only for the sake of Allah. We wish not from you reward or gratitude." If the giver of charity or the agent violates this, he may lose the reward and fall under the threat mentioned in the Almighty's saying: "And love to be praised for what they did not do." As for informing the needy that the money is charity from another person, it is not obligatory, but if it is more comforting to their hearts and easier for them, then it is better.