Questions in reverse order:  "tidally locked" means with respect to their moon.  Not their star.  Only planets very close to a star (well inside the band of the "Goldilocks" zone) can be face-locked to their star.   So, in this respect, they're talking about planets which have a moon like ours.

Twin moons should indeed mean more than one moon, though there is no requirement for them to look even remotely similar.  That said, I suspect that it's more "fluff" than actual gameplay, and I'd expect either to never see multiple moons actually implemented, or wait well into Beta to get around to fixing that.

There are no extra planets because showing all planets in a solar system would crowd up the map badly with useless stuff. Besides, it's only noticeable in Earth's system.  So StarDock picks a couple to be representative.

I haven't seen rings yet, but I know they're planned. And I would expect that Gas Giants get rings frequently, since they're really the only planets big enough to have the gravity sufficient to hold asteroid debris for ring formation.

@trims2u habitable zones around red dwarf stars are often so close that any habitable planet would be tidally locket to the hoast star, like the moon is to Earth.

I also have a further grievance with green stars. There are no actual green stars. 
Also habitable planets around blue stars(O/B type)? They don't last long enough for habitability to develop.

And purple looking starts(blue supergiants) have solar winds so strong that they prohibit the creation of planets altogether. Not even neighboring stars are able to form planet because the supergiants blow all the planetary forming material away.
It's possible that they catch rouge planets but as far as I know these stars mostly don't have any.