I wasn't quite sure on how to word the Title. My question is on Nach in Shmuel Alef, where in Perek 2 a Prophet, either Elkanah or as the Ralbag says it was Pinchas, they tell Eli, that because of Chofni and Pinchas' actions Eli's family would always die young. In the next Perek, Hashem calls to Shmuel and is informed regarding Eli's downfall, including the fate of his son. But why was this prophecy needed when it given to Eli the Perek before? Another question on this is why didn't Hashem give the message to Eli himself, if he knew already about what was going to happen to his descendant, he wouldn't of got 'upset' as he knew already?
As far as your second question, "why didn't Hashem give the message to Eli himself".
The Radak (2:27) says that since Eli was old, he no longer received Nevuah (prophecy).
This Radak teaches us that despite that Eli has sinned, he obviously was a good person as he only lost Nevuah due to his age and not due to his actions.