For the most part, they are human aliens, with no biological differences that can be discerned. The difference is that they can interact with/control/sense energy. move objects with their minds and when necessary, convert to an energy form. In their corporeal form, the only departure from standard biology is that they need to absorb massive amounts of electrical energy once per day.
I'm an American watching this on Netflix and I've never been to Australia, so please forgive any seeming cultural ignorance on my part when I ask this: In "Good Vibrations", Amber is asked by her mother to do the laundry "first thing [in the morning], so it's got all day to dry." Don't they have driers in Australia? We even see a couple of seconds later that there is a modern washing machine in this house and something that vaguely resembles a drier on the wall next to it. My point here being, why would it take all day for the laundry to dry? The basket her mother hands her looks like it's about one load, which shouldn't take more than a couple of hours with a typical washer and drier.