Yeah, that's my understanding of them, as well.
That also answers the question of whether they can be used as desktop computers.
It's not quite what I'm trying to do, but it might work. Ideally, I could just move files directly between computers. If I have to use a NAS a bridge between the two, that's not the end of the world.
From what I understand. You have files on one computer and you want to access them with all computers. You're probably running into issues because you have Windows Home(yes I'm assuming) which is very limited in it's network functions.
I don't know how many files you need to host, but I would wager you could get by with a 12tb or less device. What you are doing is adding this NAS as another computer to house all the files accessible to all computers on the network. I don't know what part of this is not what you are trying to do. Aside from spending money and adding new equipment.
The NAS will act as your new file hosting computer and depending on the hardware, will add speed and safety to your files.
If you're hard bent on not buying a NAS, look for some type of file sharing software. In that area I can't help. The only program I know of is PLEX. I would suggest looking to an AV forum for answers.