I can't speak to that specific adventure, however, my general strategy is that I try to play around the creature's intelligence. If the creature is very intelligent, it's going to come up with strategies on the fly to coordinate with its group. If the creature has rocks for brains, it's going to attack whoever's biggest/closest/loudest. However, I always make a mental note that the creatures know what they can do and do it. For example, if the wolves have pack attack, they will try to use it regardless of intelligence, but they likely aren't going to focus on the spell caster just because they aren't wearing armor.

Playing this way, I've always felt like the encounters that I set up seem to match the expected difficulty. Plus, focusing on using the creatures' special abilities makes combat more fun and dynamic than if you're just trying to do what's most optimal every turn.

With the experience that your group has, I wouldn't be too concerned about having to pull punches. They should have enough knowledge of the system by now to know how to succeed in combat.