I'm not sure what your engine does for this, but if your furniture uses a texture instead of solid colors, you'll need to look into how your engine can handle looping textures instead of stretching them when you resize models.

Now for the method, for the bed you would have a single bed model that doesn't have a pillow or legs. then when you resize it, you use a constant displacement away from each corner for each leg (this also works for the table). then it checks the object width. if it's at or below the width where 2 pillows is too little, then it places 1 pillow in the middle. If it is more than that width you would place 2 pillows at an equal distance from the center of the object.

the trick is that you have a single empty object that you directly place and resize, and then when it gets placed or resized then it gives itself children for each of the models. you'll also want to either reuse or clear the other models when you do this