How damages from an attack applies to a player?
All combat damage happens at the same time, barring abilities such as first strike. That means player 3 gains 9 life from the attack (and player 1 ends up at -8 life before losing).

From the CR:


  510.2. Second, all combat damage that’s been assigned is dealt simultaneously. This turn-based action doesn’t use the stack. No player has the chance to cast spells or activate abilities between the time combat damage is assigned and the time it’s dealt.