interesting strategy...not going to make you friends but clearly works.
only 2 reasons for standby on bolt (i don't believe they allow overbooking): the pax were either were unable to buy a ticket online and are trying to buy one on the spot, or pax were late to their ticketed bus. in either case, they are at the mercy of boltbus, and since you bought 2 tickets, you shouldn't be forced to give one up for standbys.
that being said, this is also the nicest budget nyc-bos transport option (relative to greyhound, megabus, and lucky star), and you're traveling on peak time. just because you can legally do it doesn't mean people aren't gonna be pissed, unless you have like a medical claim or something.