What is "Bala"?
Rashi citing Menachem: This is [destroying,] like "Heshiv Yado mi'Bale'a" (Eichah 2:8). Radak - Hashem should destroy Achitofel's tongue.
What is "Palag Leshonam"?
Rashi: He separated them, lest people hear them.
Rashi citing Menachem: Palag is an expression of dividing. Radak - there should be dissension among Achitofel and his colleagues counseling (Avshalom); this will confound their conspiracy and counsel. David said "Sakel Na Es Atzas Achitofel" (Shmuel II, 15:31).
Malbim: If their counsel is divided into two factions, it will be annulled, and they will not follow Achitofel's counsel.
What is the "Chamas v'Riv", and how did David see it?
Radak: It is people who conspired with [Avshalom]. This is great Chamas, for they quarrel with me. He saw in his heart.
Malbim: The informer told me that those rebelling against Malchus Beis David already reached the city.