Currently Starlink doesn't do Satelite-Satelite communication, so you'd have to downlink reasonably close to Tonga. Even ignoring the lack of downlink equipment

Currently Starlink doesn't do Satelite-Satelite communication, so you'd have to downlink reasonably close to Tonga. Even ignoring the lack of downlink equipment, the maximum range is about 250 miles. Fiji is the nearest realistic location to downlink, Suva, where many cables land (including the cable from Tonga). It's 466 miles, way over the horizon.