They're designed for 4, and if you're using the standard XP system then you'll need to make some tweaks for a larger group or they won't advance quickly enough. Alternatively you can add in some side adventures, something Kingmaker is well suited for.
Take a look at the sticky at the top for some very good 6-player conversions of the encounters. I have been running it for a group of 5, which has now become a group of 6, so I've used a mix of original and upgraded bits.