The skipper's sleeping arrangement depends entirely on the boat's layout, so this is something you need to clarify before you book—don't assume [1].
On many four-cabin catamarans in Croatia, there's a dedicated skipper's berth, usually a single bunk tucked into the forward cabin. That means your group gets all the guest cabins to yourselves, which is ideal. But not every boat has this setup [1].
If there's no dedicated skipper cabin, your skipper will either take one of the double cabins (which cuts into your available guest space) or sleep on the saloon settee. On a six-to-eight person charter, losing a cabin matters. It's the difference between everyone having their own bunk and someone doubling up.
When you're comparing boats or talking to a charter company, ask directly: "Does this boat have a dedicated skipper's berth, or will the skipper use one of the guest cabins?" If it's the latter, factor that into your group size and pricing. Some operators are upfront about it; others aren't unless you ask.
If you're torn between different boats and one has a dedicated skipper cabin while another doesn't, take that seriously. It affects both comfort and the actual cost per person when you do the math.
Meals are usually handled at the start of the week. You either include the skipper in your provisioning budget and cook for him like any crew member, or you agree on a simple daily meal allowance. Either way, it's a conversation to have before you cast off [1].