It seems like another "of" is missing. I would say as a native speaker, He is the father of two of Zofie's sons. Or of Zofie's two sons. Unless there are two Zofies in which case I would change it to two Zofies' sons.
There is definitely an error here. No one who speaks English as a native would say it the given way. Denise has the right of it: in her first example there is an implication that Žofie has more sons with someone else, in the second that there are two and "he" is their father.