Open the joint editor and click on the actor you want to adjust. A green cross will appear.

That's the joint center. Just drag it around or type in new coordinates. For the doors, you want the joint center at one of the edges acting like a hinge.

(Try the three-port view so you can better see what you're doing)

The windows should be fine as long as you just want them to slide open in one direction.

 

For the materials: A MAT pose or a mc6 file can't change the materials of parented props.

So you'd need MAT poses or mc6 files for each window.

But a single MAT pose or mc6 file can change the materials of all actors of a single figure.

So, if your house is a figure, you can swap all materials with a single mouseclick.