For the first of these four, the name, meaning 'grey-green', is obviously suitable in view of his maritime nature. For the son of Sisyphus the name will also have connotations of the sea, since this Glaucus (in one story) leaped into the sea in grief for Melicertes (the son of Athamas).
For the son of Minos, however, we must find a different explanation, since his chief claim to fame was that he chased a mouse, as a small child, and fell into a jar of honey and drowned in it. We cannot really see a 'grey-green sea' in this, so the best thing is to change the origin to glaux, glaucos, 'owl', for owls, after all, chase mice!
In general, however, Glaucus is a name that either denotes the sea or else has its primary sense of 'gleaming', 'bright' (as it did for Glauce) to indicate either a 'bright' future or the 'bright' eyes of a healthy and active person.
