The court heard that the attack had its roots in a feud between the TN1 (Trust No-One) gang from the Tulse Hill area of south London and Brixton-based GAS (Guns and Shanks).
Idiabeta and Okusanya were members of the TN1 group out to avenge one of their number who had been stabbed in a bus garage attack carried out by the GAS gang earlier in the day.
Kwame's father Kwaku, a sports journalist, told the court in a statement that his son was full of potential.
He was in the sixth form of Forest Hill School and excelled in sport, music and acting and was ambitious.
Mr Ofosu-Asare said: "Kwame was a very vibrant, energetic and enthusiastic boy.
"His brother and sister are struggling to cope with his death. All our lives have been ruined."