Hi @paulo1976
It is not possible to assess whether the Ausländerbehörde is correct or not without knowing the ages of your children and your rent costs.
In order to get 25b, your net monthly income must cover more than half of what your family needs to live on. The amount of what a family needs to live on is calculated by checking how much they would get if in receipt of benefits from Jobcenter. As your lowest net income in the period was €1890, the maximum amount that can be required by your family without it being an issue for 25b is €3780.
The monthly amount in 2024 for you and your wife is €506 each.
For children up to age 5 it is €357, for children ages 6-13 it is €390 and for children 14-17 it is €451.
As an example, if you have two children between the ages of 6-13 and two between 14-17, along with rent costs of €850, the benefits from Jobcenter would be as follows.
506 + 506 + 390 + 390 + 451 + 451 + 850 = €3544
In this case, you would need to earn more than €1772 per month for 25b.
I advise you to check the calculation yourself and if it is incorrect to appeal the decision.
Best,
Éanna