There's also a brief callback to them far later in the game too, at the beginning of Shadowbringers' story (spoilered for new players)-
when you arrive in the First your character wakes up to a merchant standing over them who very closely resembles one of the merchant brothers from the beginning of ARR, with the insinuation that he's the ARR merchant's 'soul fragment' incarnation on the First.
Unfortunately, no sooner do you part ways with him that he quickly meets a very sticky end - he's assumed to have either been killed by a sineater or been turned into one himself (a sineater attacks at the gates of the Crystarium that is then quickly killed by Lyna and the Crystarium guard, which leaves behind a distinctive ring that the WoL recognized as that merchant was wearing, seeming to hint that the sineater was them, or had eaten them).
Either way, it was a further interesting, if somewhat tragic, reference to the merchant brothers from the start of ARR.