Hm, separately or as a prefab the show up perfectly.

Here is the folder with the files:

http://www.puppenheim.org/gartenhaus8b_als_wmb.zip

http://www.puppenheim.org/
http://www.wuerfels-welt.de
Old Game Tutorial: http://www.puppenheim.org/MITutorial.zip
Free Game Editor: http://puppenheim.org/AlienalsWeihnachtsmann.zip
http://www.puppenheim.org/blender_starting_main_settings.txt