Nice to hear from you again.
1. I don't see why they should deny you to marry. Getting married and the Dublin procedure are two processes that are not directly linked to each other. But of course you can't proceed getting married if you have been sent back to the Netherlands.
2. +3. As I said above these two processes are not really having an effect on each other. After your wedding, your Dublin procedure will go on. May I ask if your fiancé is a German citizen? If yes, you can apply for a residence permit at Ausländerbehörde afterwards. I think receiving it will stop your Dublin case because it legalizes your stay.
4. What Ausweis are we talking about exactly? Your Aufenthaltsgestattung/Duldung, your home country's ID or something else?