We always use Island Birds between STT or SJU and VG. You clear customs at the VG airport.

If any of your party is returning home thru the STT airport, make sure they have three hours from the time they get to the airport to their flight time. STT is a fearful place and the lines can be epic. For example, last trip the PreCheck line was much longer than the regular screening line so even though we have precheck, we went thru the regular line. The screener insisted we must use the precheck, I stood my ground and he let us thru.