I have trip reports from my two charters on my blog -- here are the links: 2019 Charter and 2017 Charter. Like your friends, we'd spent months in the Exumas on our own boat, so chartering there was like coming home.

Navtours has decent support, but prepare to be self-sufficient. The boat we sailed last time was pretty clapped out, and we had to do a lot of improvising. Nothing catastrophic went wrong, but they turn the boats around quickly, so the little niggling things don't always get taken care of. But heck, it's a BOAT!

As for seasickness, whether it happens on the crossing depends on the conditions and you. Be prepared!