What is the ruling of the Sharia regarding informing one's brother about accusations made against their uncle, out of fear of falling into backbiting, especially given that the uncle is known for lying?

It is impermissible to accuse one's paternal uncle of adultery based solely on people's talk and rumors without proof, as this constitutes unlawful slander (qadhf). Similarly, it is forbidden for the paternal uncle to accuse your brother of committing an abomination and spreading such a claim. He should be advised to cease this action. If he does not comply, one may inform someone who has influence over him. It is not advisable to inform the brother of this, as he will be hurt. Scholars have recommended concealing evil spoken about a person if there is no benefit in informing him, as occurred with the Mother of the Believers, Aisha, during the incident of the Slander (Ifk).