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."
More top news
Tencho Hristov ignored warnings and got trapped between barriers at Roydon in Essex.
The 6km bike track will include 130m of the South Circular near Kew Bridge.
The unfortunate officer was taken to a central London hospital for treatment and his condition is not life-threatening.