Strange effect - Why is that?

Hi! I am trying to learn a little about UE4 for architecture, using rhino to import and then edit there. This question is about strange lighting issue, basically there 6 cabinets are all the exact same shape duplicated. I have no idea why the hell all of them have these dark parts in the edges? Also, anyone understand why the two bottom ones to the right are very bright then the other ones are dark? The lights that are going in are not put upon them to motivate this great change in color.0d19f3a52b50d3d9bb79ffbbfc98ab2b0e4affdb.jpeg

Basically these are just boxes with a 1-2 cm offset to create a poor looking separation so it should be a lot more uniform.

(PS: Side question; How do I add transparency to a material? I imported the default glass one but would like to be able to edit that myself later, in vray and other render things it is usually quite easy to add transparency of different sorts, then later you can edit more complicated values such as shadows, emission light etc but I recommend a more logic process putting on transparency for noobies such as me!!)

(PS2: How would I go about making the sun bigger, meaning that the shadow would be more gradual then what it is in the image? The shadow is quite sharp.