I'm not sure if this is a nightmare I've had since I was young, because I'm pretty sure I saw this on TV. Anyway, the plot goes something like this:
There's this big mansion, I think it's wine-red, out in the middle of nowhere (in a forest, to be exact). A family, or a group of people in different ages, move in. Weird things start happening. I'm not sure if the kids are possessed, or if they get possessed by the time they've settled in, but there's mostly things going on with them... I think. The adults start going loco, and some of them commit suicide. It's kinda like in the movie Shrooms where you think "the main character" is a victim like everyone else in the group, but in the end you're like 'aha, so she was the murderer', because you assume that there are strange creatures killing them or whatever. Anyway, the monsters in my (hopefully not) nightmare are like... swamp monsters? I don't even know. They look like it. One is red and the other one is green. I think the red one is in the house, while the green one is outside. They seem friendly towards the kids, as far as I know... I didn't watch much of it since I got scared.
It's the one thing I keep dreaming about, which is weird, because I can't find any information about it. No one else I know has seen it either. Also, I saw the movie around 2005 and the only fitting genre I can think of is psychological horror. It basically screws you over.