Hi, aekkara, first, Mark mentioned that wild camping is not allowed. You probably don't know what that is, but basically it's camping wherever you want to, regardless of whether it's a legal camping place or not. I'm sure you had no intention of doing that, but I'm just explaining what it means.
Second, I'm wondering why you're flying into Berlin if you're leaving there right away. If you haven't already booked your tickets, I would strongly suggest that you fly into Amsterdam instead and then fly home from Berlin. That way you won't have to deal with a vehicle while you're in Amsterdam and you'll avoid having to pay for a motor vehicle that you really can't use that much for several days while you're in that area. You could pick up the car in Cologne or even in Baden-Württemberg. Yes, there will be an extra charge because you're picking it up in one place and dropping it off in another, but as long as it's in the same country, it shouldn't be that much. You'll more than make up for the savings of not having that extra three days at the beginning to pay for.
I also agree with Mark in that you are doing a lot of driving and not spending very much time in each place. I think the most you've got is two days in Berlin and then your time in Amsterdam. If it were me, I would cut out Amsterdam. I like the city a lot, but it's a bit out of your way and this way you could focus just on Germany. I find it interesting that you're spending more time at Europa Park than you are in Munich. Munich is a lovely city and very iconic and well worth more than a day. I don't think you need much more than a day, maybe two or three days, but leaving Amsterdam off would allow that. It's a shame that you only have a couple of days in Berlin as well.
But ultimately, this is your trip, so if you're good with this itinerary, then you should hang on to it. There are problems you might face with this itinerary, but nothing is insurmountable. That said, I really would suggest not picking up your car in Berlin but waiting until you get back to Germany from Amsterdam. You do not want to deal with a camper van in Amsterdam. I can definitely tell you that.
Edit:. I'm adding this because I just realized that you said camper van. Of course I read that, and it just hit me. So you are planning on sleeping in this camper van? All five of you? Have you plotted out your places to stay yet? If you are sleeping there, I guess that would avoid a little bit of the problem with Amsterdam, although I'm not sure where you would park a camper van in Amsterdam.
If you haven't yet figured out where you're going to sleep, I would focus on that. If you decide to stick with Amsterdam, I would post something on the Netherlands forum separately and ask about where you can park your camper van and where you can stay and so on.
