thank you for joining us in the community. As for your questions:
1. Yes, he will have to take the interview in Germany.
2. With the child being somewhere else might pose a problem- in such that it will take more time to process all the case together.
Here could be onke solution that he brings through family unification his daughter to Germanyand then you apply for visa to the US.
The US authorities have more rigid immigration laws now.
I hope I could help you, if more guidance is needed please feel free to use the platform.