thank you for sharing your situation with us.
As for your question:
- since your visa expired you are not legally here in Germany
- you have two options in order to get married:
1. try to get an extention of the visa( very hard), as it is already expired
2. seek asylum and while waituing you both can process your marriage documents and you would have legal papers to stay as long as the asylum is not decided upon.
I hope we could address your questions, if you need further guidance please do not hesitate to contact the community.