Yes, is there a link to a website with dimensions and other info like photos of interior layout?
Some Marans get along great in a flock of just Marans, some have issues even if it is all Marans. Some Wyandottes get along great in a flock of just Wyandotte's, some have issues even if it is all Wyandottes. Some flocks with both Marans and Wyandottes in it get along great, some have issues. I would not let worries about how these two breeds might possibly interact prevent me from getting them if I wanted them. The breed is hardly ever (if ever) the issue. The personality of the individual chicken might be.
One way to greatly reduce the chance of having behavioral issues is to not crowd the birds. Instead of asking how many can I fit in this space think of how many you want and then provide enough room for that many. I'm glad you asked before you got that coop. You are right to be concerned, usually the numbers mentioned for a prebuilt coop are greatly inflated.
A lot of how much room you need, other than just luck with their individual personalities, is how you manage them and your climate. Some people like to give you magic numbers as if that solves all problems and guarantees eternal bliss. One problem with that is that I've seen people give anything from 1 square foot per chicken to 15 as the minimum required. That may or may not take into consideration anything about the run. Who do you believe? What do you believe?
If you wish you can follow the link in my signature to see some of the things I think make up space requirements. I don't like to think of the coop in isolation. Chickens do not recognize a difference in coop space versus run space versus total free ranging. Those are human concepts. Chickens just recognize whether or not they have sufficient space when they need it. I like to look at the space provided by your system.
You are in Norway, thanks for providing that information. That means you will have some pretty snowy winters and probably a few stormy days. Chickens can get used to snow but they often don't like it much. There is a good chance yours will wind up spending quite a bit of time inside the coop in your winters or you can provide some protected area outside the coop to increase their room. You are going to need more inside or protected room than I will because of your climate.
Before I would even begin to guess how much room you need I'd want to know the number of chickens you actually want, the size of the coop, how much room they have available outside the coop, when they will have access to that outside room (will you leave them locked in the coop section alone until way late in the day), will you have roosters, will you be integrating new chicks later, and will a broody hen raise chicks with the flock. That's all I can think of right now, you've given your climate.
One of my favorite concepts is to make this convenient and easy for you. With enough hard work and stress you can usually squeeze chickens into a fairly tight space, But why make your life harder than you need to?