Your one night in STT is on the 27th then? If so, I would try to test very early on the 26th for both USVI and BVI entry. Upload to the portal immediately after getting results. You should have your green code by that night.
Alternately you could test for USVI entry on the 25th and then test at your hotel in STT for BVI entry but that feels a bit risky too.
You should try to avoid getting tested in the BVI if possible.