For those unfamiliar with the meaning of V2:
Main clauses start with the topic. It's whatever you want to stress (in this case maybe). If there is nothing you want to stress in particular, it's the subject. The main verb of the sentence comes second (hence V2).
(In German and Dutch this is normally just a single word even if the predicate consists of several words as in English have been. The remainder of the predicate comes at the end of the sentence, after everything else. But the Scandinavian languages handle this differently.)
V2 is an intermediate stage between the original Germanic word order (very free, but usually the verb came last) and SVO word order, to which all the Germanic languages are moving. English is almost there, but still has some vestiges of V2 (example: "Little did I know...").
Icelandic is generally not considered a Scandinavian language because it is not spoken in Scandinavia and due to Iceland's relative isolation is also quite a bit different - much more conservative. Apparently, modern native Icelandic speakers can still understand the old sagas in the original language. However, the Scandinavian languages are related with Icelandic and Faroese (which is closely related to both Icelandic and Norwegian). Together they form the North Germanic languages.
North Germanic is one of only two major branches of the Germanic languages. The other, West Germanic, consists of English, Dutch, Afrikaans, German and some smaller ones including Scots, Frisian, Yiddish and Luxembourgish. (As usual, in some cases it's debatable whether something is a separate language or a dialect.)
A third branch, East Germanic, consisted of Gothic and possibly Vandalic and Burgundian. It was last attested in the late 18th century and apparently went distinct when its last speakers in the Crimea switched from Gothic to Tatar and/or Greek.
That sounds like a fringe theory. It is generally accepted that Hungarian, Finnish and Estonian are in a common family called Finno-Ugric languages, along with some other Uralic languages. If you have good evidence that this is not the case, you should probably start by getting the academic community to accept it and to rewrite the books accordingly, not by contradicting people in a Duolingo discussion.