Jamieson, Fausset and Brown on 1 Samuel 31:6

6. So Saul died--(see on 1Ch 10:13; Ho 13:11).

and his three sons--The influence of a directing Providence is evidently to be traced in permitting the death of Saul's three eldest and most energetic sons, particularly that of Jonathan, for whom, had he survived his father, a strong party would undoubtedly have risen and thus obstructed the path of David to the throne.

and all his men, that same day together--his servants or bodyguard (1Ch 10:6).