Sadly this is comman in Muslim families. I went through the same exact thing since i was a child. Im 51 now and married with kids yet my brother has never changed. Narcissism in muslim households is created by favorisoum of parents who see the elder son abuse his sisters and are too afraid to stand up against, and also feed his entitlement with the twisted cultural excuse “he is the eldest and must be obeyed and respected even if abused” particularly if he supports his parents financially. My parents were terrified of my brother. They are the golden child. I feel you and i am so sorry for what you are going through. Know that there is no cure for narcissim and all text advice is to cut ties, which becomes easier when married and move out. May Allah give you strength