Ok, lemme start off by saying what a soul is. A soul is a body and a spirit combined, any living thing is a soul, humans are souls, animals are souls, ect. When Lucifer and the Fallen made refuge in Hell, they used a dark energy called magick to create "angels" of their own, and of course, God knew this and would have none of it. So the magick made horrible monsters, a combo of animals, plants, humans, and other stuff, and brought them to life. They were each given some powers and boom, demons. However, they are spirits, but yet they aren't. It's complicated. They're a mass of dark energy, while an angel is a mass of light energy, humans and animals being what is called gray energy, neither dark nor light, neutral.
So, yes a demon is a spirit, but at the same time a demon is a demon. It's hard to explain really XD
And as for aliens, while I doubt few if any have visited the earth (if they did, they probably went "EW!" and left) there is evidence within the Bible and in the universe of other living beings out there. In the Bible, the first line in Genesis (Often left out of most Bibles) is "And the lord spoke unto his servant Moses, saying "Behold, I reveal unto you concerning this Heaven and this Earth, write that which I speak." A little odd how he says THIS Earth, right? Could it be there's other Earths out there? Not only that, but astrologists have confirmed that there are other planets not far from here capable of sustaining life, and that's just nearby! Who knows what else could be billions of lightyears away?
As for the Lesser Key of Solomon, I've not read it, I've only skimmed through the original, but it was stolen from me years ago. The runes, symbols, seals, and summoning circles are somewhat correct, however, I remember there being a lacking of something, but I doubt I'll be able to recall what it is unless I get another copy of the book. I would look it up online, but the internet changes things, it's hard to trust. Pretty bad when Satanists can't even get their own religion right because they went off and googled everything :/ And, as I said, I'm still in the midst of studying macigk and the occult, it's a very extensive study too XD