Correct solutions to the first part of the question were received from: Alastair H (Forres Academy), Andrei L (School 205, Bucharest). The solution below is based on Andrei's submission. Well done to both of you.
First I created a small cube from the net in the figure and observed the cubes from the problem:
The first cube cannot be formed from that net, because the square marked with a red arrow should be in the position marked with a blue arrow:
Looking at the cube made from the net: It is possible to see that the second cube (horizontally) can be made from that net and also the last three
In conclusion, the 4 cubes denominated before are the same one, created from the net (B, D, E and F below).
The second part of the problem:
First shade the three faces of the view B of the cube which are not visible. Then do the same with the other three views of the same cube (D,E and F).
A B C D E F
You end up shading all the faces. This means that you can see all the faces of the cube in the four views B, D, E and F so there are no hidden faces where you can shade additional sections.