[richalex2010]

For Groene07: It shouldn't be. Select the part that is below the other, and see if it already has keyframes (along the time slider at the bottom). If it does, delete them, and scrub through. If that's not the case, I'm not sure what I can tell you... maybe try to post a video (screen capture or rendering, whichever is easier - it doesn't need to look good to be able to tell what the problem is).

For JRosslet: As far as I know, it would require either some clever scripting or manual animating. Manual is probably going to be easier, unless there is a lot you need to do this to.

Something to consider... you only need it to look good from where the camera is. If you don't intend on any shots inside a building, you don't need to model the inside, for example.