Is it permissible for the younger brother (who is three years younger than his sister) to approve or reject a suitor proposing to his 26-year-old sister, knowing that he uses coercion and force?

If the sister has no guardian other than her mature brother, he has the right to object to an unsuitable suitor. However, he does not have this right if the suitor is suitable and the sister consents to him, and she may refer the matter to the judiciary if he prevents her. But if she has a closer guardian, such as a father, the brother does not have the right to prevent her; rather, he can offer advice and express his opinion about the suitor without compulsion. The relationship between siblings should be built on mercy and respect, and discussions should be conducted with wisdom and gentleness.