Seeing the destruction of his army by the enormous Kumbhakarna, Rama turned to him with his bow and arrow. There was a fierce battle between the two. In the end Rama used his amogh arrows (that never miss their mark) to kill Kumbhakarna and broke his body into two pieces.
Ravana lamented the death of his brave, beloved brother. His sons Atikaya, Narantaka and Devantaka tried to console him. They told him that he should be assured by their presence. We will destroy Rama and his entire army in the battlefield they said so Ravana allowed them to go to battle.
Atikaya, Narantaka and Devantaka entered the battlefield with blood curdling roars and angry cries.
Lakshman came forward to prevent the killing of their forces. Atikaya challenged Lakshman to fight. There was a terrible battle but in the end, Narantaka and Devantaka were killed.
Death of Khumbkaran, Ramayana – The Epic Story