Ban for 5 years.. accused of using false documents

If you are legally married and that marriage is not suspected of being a sham, a spouse's right to live with his family should allow a family reunification. But with a history of fake documents, it might be difficult to overcome the suspicion that the marriage is fake as well. The advice in the comments is good, your German friend should talk to an immigration lawyer in Germany.

You will need an immigration lawyer to handle your case.

First of all, it does not matter if you are innocent or not. From what you are writing, it sounds as if you were accused of a crime, failed to meet in court, were convicted in absentia and failed to lodge an appeal. You are now convicted and the deadline for an appeal has lapsed. There is nothing you can do about that now, if you failed to face the charges earlier.

You can apply for a family reunification visa even if there is an entry ban in effect against you, but it is of course not self-evident that the visa is granted. If a visa is granted, the entry ban will be reduced or suspended. On a case-by-case basis, your rights to sustain a family relationship will be judged against any risk you (seemingly) impose on the society if you are let back into Germany. IANAL: Working illegaly might not be a reason to uphold the entry ban, but document fraud is a severe crime in Germany. Honestly, you must expect your visa application to be refused and that you will need an immigration lawyer to lodge an appeal for you.

I say again: You will need an immigration lawyer to handle your case.

If you get married, you can get a Aufenthaltserlaubnis für Ehepartner and can for sure come to Germany, but germans dont forget and since you have a criminal background here, soon or later the police will knock your door to make you pay/explain for what you did or not about falsing documents.