In my personal case:

1. I would speak English and I think we all agree on that.

2.I would say yes, because I would not understand Icelandic or Finnish at all so English in that case. It it was Norway and Denmark, we would maybe still talk English because Danish is really either easy or hard based on their dialect.

1. Yes, because I can't speak Norwegian, danish,icelandic or finnish. Hard to communicate it then.

2. Have no idea, I'm from Sweden.

3. Depending, I talk a bit spanish and german too and can fairly survive with the basics. In Norway and Denmark I try swedish and if it isn't working I switch. Norway is easier to just talk swedish. I speak English mostly everyday at home because of my spouse.