Residence permit for children

[kon23]

Hello,
My father has been working in germany for 3 years.Now that my mother has also decided to move there he is taking my 11 years old brother with him too. My father already has a residence permit and we come from a non-EU country. Once my brother arrived in Germany, my father took him to the office for foreigners authority(Ausländerbehörde). They required some documents from my father and after he provided them they told him that he should have got a visa for my brother at first. We did not know this and by the time they told us my brothers stay in Germany was completing 3 months. To make matters even worse his passport had expired and we had applied for a new passport so in the meantime he could not move from Germany. After this my father talked to them and they said my brother could do the visa application in Germany. However a few days ago they sent us a letter stating that my brother was illegally in Germany and my father had to make a statement regarding this issue. So they asked for a letter explaining the situation and why my brother should stay in Germany. We went to a lawyer and she said it is too complicated and she would not deal with it.However the office for foreigners authority has not made a final decision so theres still hope. Can anyone help me with the letter please as in what to include?
Thank you very much

[mgb]

Did the father apply for a residence permit for his son?
Where is the mother and who could accompany the child if a visa in the home country is needed?

[kon23]

Yes he took him to take a residence permit but they said later that he needed a visa. The mother is in Germany as well but if he needs a visa the father will take him to his country. Problem is the child is past the 3-months time he can stay in Schengen area due to the passport issue.

[mgb]

Did they deny the residence permit application in writing?
If not the child is not illegal in Germany.
On the other side if both parents are in Germany it is not reasonable to send the child back to his home country for a visa.

[kon23]

They have not yet taken a final verdict. They asked for some documents whether the father can sustain him and the letter explaining the situation.