How to negotiate a salary in Norway/Scandinavian countries?
I'm a PhD student, born and raised in Denmark. I have not applied for jobs in Norway, but have done some teaching in Norway and had a few interactions with Norwegian academics. 

The Norwegians will appreciate humbleness, good manners and honesty. In the culture, it is very acceptable to care for your family. 
In all communications in particular, good manners is key. 

My recommended approach: Be humble and grateful for their offer, state all the reasons why you really want to work with them, then, without overdoing this (remain humble) state all the reasons that you are valuable. Then, proceed with honesty: state that you want to be at their workplace, how much you want to get paid, that you have some experience and that you need some funding to support your family.

Wish you luck!