First unless its just the photos your ground texture looks like its being mipmapped since it looks blurry unless thats just the camera angle a extra 1 flag behind your object loading with set mipmap off.
Load object "scene.x",1,1
And for the trees i would suggest what Image all said.
Set object transparency tree,3 or 4
There are 4 levels of transparency 3 and 4 being better for foliage and trees.
Plane may also be the same problem as the ground issue the texture of is mipmapped.
As for the walls i have no idea on that one.
Like Seppuku Arts said you should really have everything as separate models that way if you need to change the look or add a effect to get a desired look you can without affecting other objects and if a object is not loading the way you want you can rework that single object not have to do the whole scene.
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