Welcome to the Wefugees Community and sorry for the late reply.
Unfortunately, family reunification is in the most cases a quite long and nerve stretching procedure.
Regarding identity verification, I assume that the German authorities wanted to double check your documents, right? But as you had the interview already and your documents have been legalized an approved, from my point of view, waiting for the visa issuing is everything you can do right now. The waiting time also varies from embassy to embassy (consulate).
In the meantime, you might have received an answer already!?
Please feel free to update or get back to us with any further questions.
All the best,