Has didn't have something to hold to the captured soldiers of Vego. But he had to trust them to this mission. The moment they will turn their back on him, he doesn't have a backup plan except for his explosives. Which he didn't really want to use. He needed the Vego's wealth and resources.
They brought minimum food supplies because he wanted his men to hunt for their food on their way. So he won't use too much of Novalia's resources.
Novalia has plenty of resources, but he spent his money on labor.
His actual plan is to befriend Vego and not destroy them. He will sell ammunition to them. Vego will make him a rich man.
They encountered several storms on their way. Luckily, they found some unhabituated islands, that's why they safely dock their ships.
Rocco was thankful for the crowned prince's change of strategy. He doesn't need to kill his brothers.
