Hi @kobs
Have you specifically contacted lawyers for immigration law? In German this is variously called Migrationsrecht/ Aufenthaltsrecht/ Ausländerecht.
You can search this database of lawyers in Germany for someone with this specialisation:
https://anwaltauskunft.de/anwaltssuche
I checked in Prenzlau but did not find anyone. You may need to **** further afield, e.g. in Berlin.
Alternatively, you can first contact the organisation Johanniter, who have an office helping migrants in Prenzlau. They also assist people who have need to have their residency status clarified. Their help is for free and I presume someone there will speak English:
https://***-johanniter-de.translate.goog/dienste-leistungen/angebote-fuer-privatpersonen/lokale-angebote/dienstleistung/migrationsfachdienst-1828/?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=wapp
To get married, you contact the registry office (Standesamt) in Prenzlau:
https://***-prenzlau-eu.translate.goog/sixcms/detail.php/52965?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=wapp
You will need to provide your passports and birth certificates, possibly other documents. Your partner will have to provide a document from the Polish authorities confirming she is eligible to marry. Whether you need to do this depends on your country of nationality.
The Standesamt will inform the Ausländerbehörde (immigration office) that you are in Germany without a legal permit. You can request a temporary paper called a Duldung if the marriage is due to take place soon. I therefore recommend you prepare as thoroughly as possible for your appointment to set a marriage date with the Standeamt. You will be in an insecure position until a Duldung is issued and it is at the discretion of the authorities whether to issue you one or not..
You may face some consequences due to have been illegally resident in Germany, most likely a fine.
After the marriage, you are entitled to a residence permit as the spouse of an EU citizen.
Best,
Éanna