I can't figure out this bizarre movie...?

I think it was an early nineties film. The plot follows a couple who accidentally murder someone and then are blackmailed by this other guy who is crazy and lives in this crazy house filled with slides and toys and stuff. The couple learn that the crazy guy has a twin brother he accidentally let fall into a river when they were kids--this is the opening scene I believe--and the couple kidnap the twin who is now in a vegetative state to get an upper hand over the crazy guy. There is also something hidden inside a civil war diorama I believe. I know this sounds absurd, can ANYONE think of what this movie is called?