Is it permissible to take the fifty Egyptian pounds designated as charity for the deceased and return them to the giver as part of his monthly assistance without his knowledge, and will the giver and the deceased receive reward in this case, knowing the giver's dire need?

There are two important matters:

1. If your friend would not accept the Zakat if he knew it was Zakat, then do not give it to him unless you inform him of its true nature. If he accepts it, then that is fine; otherwise, give it to someone else. 2. It is not permissible for your friend to give charity as long as he is in need, for giving charity in a way that diminishes his provision is a sin, and assisting in sin is not permissible. It is also not permissible for you to resort to trickery by taking charity from him and then returning it to him, because an agent is not allowed to disobey the principal, and this violates the agency contract and the principal's intention. Furthermore, it is not permissible for you to pay charity on his behalf from Zakat funds before he takes possession of them, because Zakat funds are not owned before possession, and Zakat has specific recipients that do not include giving charity on behalf of the deceased. And if he takes possession of the Zakat, it is not permissible for you to dispose of his money without his permission.