My understanding is that yes, they still get stored in memory, but the amount should be negligible.
A quick test would be to instantiate a high number of GameObjects, let’s say 100000, and look at your memory usage, then disable them on a key press while the game is still running and check memory usage again.
Answer is NO. It is not loaded in VRAM (at least that is how the editor works, I have no idea how it is on actual platforms, I will assume it is the same but … assumption is the mother of all f###-ups). I will check if it works like that on iOS device.