Make all the lights have soft shadows,
except for the one called "Sunlight".
Give it ray traced shadows instead.
1. Select each light, one at a time, and click Light>Edit
2. Adjust each lights Shadow type.
3. Click Ok.
Preview again.
It should look like this:

Adjusting the Shadows
Now we have shadows, but they are a little too light.
1. Select each light and click Light>Edit
2. Change the Umbra Intensity on all the lights, except the one
called "Art", to zero.
3. Set the "Art" lights Umbra Intensity to .100
Preview.
It should look like this:
Now the shadows look horrible, but at least they are dark enough
to work with. They need to be softened up a little.