Hello pnunez,
So from what you describe and your screenshots that you have posted what I believe is happening is a light leaking issue. This is typically caused by multiple walls created from different objects that have been placed so that they shouldn’t allow lighting or shadows to leak through. However, this can cause problems as your lightmaps are bleeding across from one object to the other.
The easiest fix for this is to create your walls and building with one mesh. So creating a two sides box that is hollowed.
I am linking you to our lighting troubleshooting guide that should help you in case you get stuck or have any questions. This guide covers a variety of issues, not all, but should help you with this one.
Thanks,