When a spell (for example, Dauntless Onslaught) that targets more than a single target, if both of them have a reaction (Heroic, for example) to being targeted which happens first? The specific case I'm wondering about is if I have a Vanguard of Brimaz and a Phalanx Leader, the order in which they are triggered matters because the newly created creature token may or may not have the +1/+1 counter that Phalanx Leader could give it, though this is something that could happen with any spell or ability that has multiple targets, where there are multiple thigns that could be triggered in some way by the effect of the spell.
Vanguard of Brimaz and Phalanx Leader trigger on the spell being cast. There's only one spell being cast, so their abilities trigger simultaneously. The next time a player would get priority, you get to place the triggered abilities on the stack in the order you desire. (If the abilities of more than one player triggered simultaneously, each player starting with the with active player would place their abilities on the stack in the order of their choice.) They resolve in the opposite order (last in, first out), so you'd place Phalanx Leader's ability on the stack first.