The amount of life a player can lose is not bounded by their life total. For example, if your opponents have 1, 2, and 10 life, respectively, when this scheme’s ability resolves, each of them will lose 3 life. This brings their life totals to -2, -1, and 7 life, respectively. You gain 9 life. Then the first two opponents lose the game as a state-based action. (If the first two opponents concede before the triggered ability resolves, however, you’ll gain only 3 life.)