The party I run just finished up Chapter 1. They started with 4 or 5 PCs and now we have 7 (up to 8 depending who shows up). The average level is still 2+. During the Malachite Fortress I did double up on some of the hobgoblins but otherwise, most everything was left as is. There was some bottlenecking but that's the problem with a big party.
Looking towards Chapter 2, I would expect to have a lot more goblins available and add them as need be to toughen up the fight. The encounter with Drakthar will probably have more underlings with him also.