Not sure, if i understand you correct, but if you want something to not cast any shadows, you just can turn off a switch, so that this particular object won´t cast any shadows at all.
If you just want the shadows to be less dark, but still there, then you would have to lighten up the interior room, with additional light sources.
Or, if you use a skylight, you can increase it´s intensity scale, which basically pumps more area light into your room/world.
(however, this might have some other side effects, so you have to test, if this works for your scenario)