Copenhagen to Norway summer 2024

Decide which days you want to do this and then go to the websites to see what is available.

I highly doubt anything is sold out already but the best way to find out is to do a dummy booking.

I think everything will be readily available except lodging in the fjord area, should you decide you'd like to break the Nutshell trip mid-way. High-season lodging is tough in that area, especially in Flam. If you know your dates and think you might want to spend one night there, you'd be well-advised to make a cancellable reservation right away.

Tickets for the first main-line rail segment of the route (Oslo to Myrdal) can be considerably less expensive if purchased well in advance, and those trains can sell out if you wait until shortly before your travel day to attempt to purchase tickets.

I think the Flamsbana can sell out--though I believe not far in advance--but as far as I know, the fare doesn't vary. You can buy a ticket from Oslo all the way to Flam, including the Flamsbana, from the Norwegian rail website vy.no. That's also where you can buy the Voss-Bergen ticket; I think that part of the trip is fixed-fare.

I don't know whether the Naeroyfjord ferries sell out; I think they have fixed fares.

Overnight ferries from Stockholm to Finland can get very pricey if you don't plan ahead, so I'd expect the same might be true for Copenhagen-Oslo ferries, but I have no personal experience with those. You can take a look at fares for the next two weeks to see if they appear to be higher as you approach the travel date.

"Are we too late to make reservations for things for this summer?"

Are you talking only about ferries or are you also asking about hotels and attractions.

When are you traveling. You said summer but what month and days.

We are hoping to due July but our dates are flexible. It sounds like we might have some issues depending on where but overall we should still be able to book things. If we do the NIN and plan a stop in one location is there a city that is most recommended and good for kids?

There are no cities along the NiN route except the termination points, Oslo and Bergen. Both are very attractive. I'm not a hiker, but I know there are some good walking opportunities around both those cities. Oslo has a considerably wider variety of museums than Bergen.

The other settlements along the Nutshell route are quite small. Flam is the most frequent stopping point, I believe. There are RIB (inflatable boat) trips available from Flam, and I think also bus excursions to a viewpoint above the fjord.

Voss is the point where you get off the bus from Gudvangen (final stop of the Naeroyfjord ferry from Flam) and board the regular train on to Bergen. Voss isn't located on a fjord, but it reportedly offers outdoor activities. There is lodging available at Voss, possibly at a lower cost than in Flam, but check hotel sites carefully vis-a-vis the locations of any activities you're interested in if you don't plan to have a car.

If you have any budgetary concerns at all, try not to fall in love with the idea of any special activities until you've checked their cost; Norway is extremely expensive.

You don't have issues. Concentrate on booking accommodation then worry about transport much closer to the time. The trains are mass transit and would be useless in that role if they sold out months in advance.
Norwegian trains can only even be booked 90 days in advance, and there is no need to do so anything like that. Even down to Flam it is often inaccurately reported that they sell out. They don't- there is always unreserved capacity.
It is the same on the Copenhagen to Oslo ferries or the Stockholm to Finland ones . It is a nonsense that they sell out months in advance. Even if you have a car months ahead is way short of the mark. You will presumably be travelling as foot pax. There should almost always be on the day foot passenger tickets. Why do you think they do the cheap mini cruise tickets?- not out of the goodness of their hearts, but to fill the capacity. People don't book those mini cruises way in advance. They book them at short notice on a whim, almost.
And the Fjord ferries are also mass transit, part of the road system of Norway. They have to be available at short notice to those who actually NEED to use them- the locals.
I don't even believe that such a long tine ahead hotel capacity anywhere will be full. Start booking, but there shouldn't be problems.

The cost of the Stockholm-Turku ferry I took increased from the equivalent of about $85 (US) to over $200 by the time I bought my ticket. The Copenhagen-Oslo trip is longer and probably consistently more expensive. I haven't paid attention to the fare on that run in the past, but these are the current prices on the DFDS website for the cheapest inside cabin for two people on Pearl Seaways:

Travel Date.......Fare
Dec 26...............€322
Jan 2...................€140
Jan 16....................€91
Jan 30..................€70

Those are all Tuesday sailing dates. Fares on Friday and Saturday nights seem a lot higher, and Thursday and Sunday nights are also higher than Tuesdays.

Although large ferries may never fully sell out for foot passengers (I have no clue about that), the least expensive cabins can certainly sell out, increasing the cost for those buying tickets late. That happened to me on the Stockholm-Turku run.

As for summer rooms in Flam, it appears the starting rate for a room with a shared bath at the Brekke Gard Hostel is the equivalent of about $154 on booking.com, where I didn't find any hotel rooms listed for the ten or so random weeknights I checked in June and July. (I realize that doesn't necessarily mean all the hotels are sold out, but it's not a good sign.)

I wouldn't expect major difficulties at this point in arranging lodging in Oslo or Bergen for the summer, but rates may climb over the next few months, especially in Bergen. My 2022 experience was that Oslo had decent availability in the summer, probably due to less business travel at that time of year. However, I imagine tourist traffic will be considerably higher in 2024 than if was in 2022.

Thanks all for the feedback!