It's true that the three Scandianvian countries - Denmark & Norway & Sweden - are similar because of their shared history. Because of this, their languages are also alike and we can understand each other (to some extent) without much trouble or previous studying. The alphabet is almost identical, and a big amount of words are the same or close to be. So if a Dane, Swede and Norwegian meet and talk casually, all parts are likely to understand most of the conversation and communicate succesfully. The same with reading-writing. It's also true that Danish is said to be the hardest to pronounce correctly - I once read that the Danes pronounce words in such a unique way that something similar has only been found in an African tribe. Whether or not this is true I don't know, but it is a fact that non-Scandinavians often have more trouble learning to pronounce Danish correctly than Swedish or Norwegian. To make it easier to remember, you can think of it like this - Sweden is the singing older sister, Norway is the 'normal' middle child, while Denmark is the youngest and hardest to understand. I have heard the statement about Danes having ease with learning Icelandic before, but I haven't tried it myself, nor do I know any who can confirm it, so I can't really say anything about this.