Welcome to I’m stuck between two headcanons either
A. Prussia is germanys dad and Austria is just his uncle but was so much of a father figure he also got a dad title
B. They don’t actually know who Germanys dad is. It’s either Prussia or Austria but due to some Mama Mia type shenanigans no one actually knows. They ended up with telling everyone it was Gilbert in social situations, but like bro, Ludwig just straight up had two dads cause no one actually k n o w s