To emsquared's point, yes, 1 advantage = 1 boost to your ally; 2 advantages = 1 boost to any specific person in the group. That means you can pass 2 boosts to any one specific person for 3 advantages (next ally + "specific" ally who happens to be next ally). SIR's effects stack onto this, of course.
In the olden days of Star Wars, people often interpreted the "pass 1 boost to the next person" as something you could choose multiple times, but I believe the devs have stated that it's only possible to choose that one time in Genesys to avoid the dice-snowball effect.