I wrote: "the president is my father" and it wasn't accepted! Why?
I cannot explain why Duo declined your answer, but it is correct (now) as below. Maybe the word order changed the emphasis/meaning & spelling.
Yes it did. Başkan & başbakan.
Başkan (noun) government president.
Başbakan (noun) prime minister.
"The prime minister is my father." Başbakan benim babam.
Correct Turkish answer to your English question which I modified.