with the square room issue it looks like the face that is the issue has a flipped normal, faces only texture on one side in gameguru, if the face is the wrong way then it will render invisible, in your 3d modelling software you should be able to select the face and flip the normal, then export it back to gameguru.
It looks like the areas that have issues are single planes, is that right? If you want to be able to texture both sides then you need a face on each side (2 planes back to back) with the normal of each facing the direction you want to view the texture on.
As to the floating issue in the opening post, are each of the models made up of multiple separate objects?
It may be that the individual objects origins aren't set right, If so, then in your 3d modeller highlight all of your objects and resetting their origin points to 0, then set your rotation, location and scale.
In Blender you would switch to object mode, press A a couple of times to highlight all objects, then press shift+C to place your cursor at 0x0x0, then in the tools menu selec the origin drop down and choose origin to cursor, then you need to make sure the location, rotation, and scale are set via the ctrl+A menu.
I'm not sure how to do it other modellers, you might have to research that.
(make sure you backup your work before trying any of this, I may be wrong and you might mess up your models this way)
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