Those are the militia. They are not AI players. Those ships sole purpose is to sit there and guard the planets they are at. They are intended to be a sort of "speed bump" so players can't just spam colony ships at the beginning of the game. They will never attack you, you just need to take them out before colonizing. FYI you should try and take asteroids and dwarf planets first, because they are only guarded by two ships.

The pirates, on the other hand, will attack you, so if you have them on (may not be a good idea for the first game), beware once you hear a warning about "pirate raid is forming".

Also, if you're playing Rebellion, I've made a "open tutorial" map, in which it is impossible for the one AI player to ever leave it's homeworld. While I've made the militia harder to both give you something to fight as you develop and expose you to all the ships in Sins, you don't have to worry about coming under serious attack and can thus explore and try things out at your leisure. The one exception is again the pirates, but their attacks are predictable and for this map I'd turn them on so you can practice being on the defense.

If you're not playing Rebellion, you can turn all the AI players off, so any map can be used for this kind of game.