Generally speaking, German authorities will only accept foreign documents if they have an Apostille (basically an extra document vouching for the validity of the original document in a standardized manner) and a translation by a certified translator (of both the Apostille, that will likely be in the same language as the original document because it's from the same source and the original document).
There may be exceptions if the documents are from the EU, but I guess if you are not EU citizens, your documents will likely not be from a non-EU country.
However, if you already got your family reunion visa, you should have all those documents already, because the Ausländeramt already required them. If they didn't ask for those papers... I guess there might be some exception for you I don't know about.