Dear
@Carlis,
thank you for your question in the community and congrats for the kids.
as for your question:
1. if you intend to stay in Germany please get the Vaterschaftsanerkennung and the Sorgerechterklärung at the Jugendamt prior to the date when your papers are expiring.
If you have this two papers and the identity papers, you will receive Aufenthaltserlaubnis based on the kids.
Best regards,
Nilab