I agree. Although there's something not quite right with 4 and 5.I get that the second and third are related and the fourth and fifth are related. So, I'm guessing the sixth, unknown shape will resemble the first shape somehow. i'm just not certain exactly how it will look.
The given pieces? You mean the 5 views? Those are 5 views of a single piece/object, which is formed by fusing several small cubes.The use of the word "cubes" in the question is kinda throwing me off. A cube by definition is symmetrical and comprised of six equal squares and it's hard to see how the given pieces smoothly form "identical cubes" to be fused into some larger "object," whatever shape that might take.
You can deduce the shape of the object, by analyzing the given views. This requires some spacial aptitude. To help, I made sketches, starting with possibilities from image #5.How is it possible to deduce the shape of the object without knowing what the object is to begin with?