The Emmaus Moravian church in Coral Bay is undoubtedly the most beautiful, for building and setting, but a bit big for your group. I'd personally go for either the Bethany Moravian, or the Nazareth Lutheran-- which is right in the middle of Cruz Bay but a lovely oasis of calm. The Moravians and Lutherans both go back to the seventeen-hundreds on St. John and are the historical heart of the community. As for the logistics of arrangements, I don't know these days, but I can get you contact numbers if you want.