For the Inside and Outside lighting use Camera volumes that are configured in the Shapespark editor Camera tab. The volumes allow to have different Exposure setting for different regions of the scene, so you can have darker exterior and brighter interior.
Lighting with area lights only is not super common practice in Shapespark scenes, but sounds OK. If you could send links to a scene that has such funny shadows, we should be able to tell more if this is due to the light type, or some other factor.
How hight is the Flood dark limit setting in the scene with black splotches behind the sofa? You can try different values without baking the scene again, just use the Post process buton instead of the Bake button. This post could be also useful: Blotches and Burn Outs - #2 by wojtek