Three more teenagers have been charged with murder over an alleged attack that killed a teenage boy and seriously injured his brother in a stabbing outside a school in Sydney's west.Police previously charged two teenagers, but have now charged three more boys, after the alleged stabbing near Doonside Technology High School on Power Street about 3.40pm last Friday.Isiah Naden, 18, died of stab wounds on the pavement outside Blacktown Police Station.Naden's 19-year-old brother is in a stable condition after surgery.Before police arrived, the two injured boys drove from the school to...…Three more teenagers have been charged with murder over an alleged attack that killed a teenage boy and seriously injured his brother in a stabbing outside a school in Sydney's west.Police previously charged two teenagers, but have now charged three more boys, after the alleged stabbing near Doonside Technology High School on Power Street about 3.40pm last Friday.Isiah Naden, 18, died of stab wounds on the pavement outside Blacktown Police Station.Naden's 19-year-old brother is in a stable condition after surgery.Before police arrived, the two injured boys drove from the school to...WW…