Minecraft Nintendo Switch?

I and friends decided to buy minecraft for the nintendo switch. At first 2 friends bought it and 1 day later I and my girlfriend bought it. Now the problem the friends who got it first could play together without any problems. And then we could join 1 day later without any problems, but as soon as I create a world only my friend can join me, but also only after she clicks on join, goes to the home menu and then clicks on join again. Then she dies once because she supposedly falls from a height and then she can spawn normally.
but the other 2 friends can't join us because of the nat type it can't really be because we can join them as well as on playstation with cod fifa etc. Only with meincraft why is that?

Your friends or your friends and you / your girlfriend probably have different NAT types

But as I said, we can join them just not the other way around and in no other game does that pose a problem…

Then write to Microsoft support.