As I see, what you are mostly discussing here, is “Shared Dreams”. I must tell you, that such thing is not scientifically possible. Our brains are not some sort of connection cards which connect us to a LAN network of dreams or something. It is not physically possible, as that would be telephacy.
The dreams you’re talking about are 100% yours. They are created by your subconscious and they are controlled by your subconscious. If you become lucid, you may control them as well, however, major part of the dream, the dream characters would still be under the control of your subconscious. Therefore, there is a lot of possibilities, how those characters could act like. They can be angry and threatening, as you say, or friendly. Most of their actions depend on your expectations. If you expect them to act like DC’s in the “Inception” movie, they will do that, and possibly, make you wake up. So, the reason, in my opinion, is that you are looking too serious at movies like “Inception”. Remember, that’s just a movie, full of fantasies, just like our dreams. If you look serious at such things, they will happen in your dreams. Dreams are controlled by our minds and therefore, you should make sure that your mind is clean of such nonsense as Dream hackers, Shared dreams etc. That’s my opinion, yours may be different.