In english you have to put in the definite or indefinite article the big armchair or a big armchair
Or make it plural, "who has big armchairs?"
To me it doesn't sound normal in Hungarian either.
Kinek van egy nagy fotele?
Of course in certain contexts it may make some sense to drop the egy, but I guess the same can be said about English as well.
Isn't fotelje ?
No, fotele is correct. In many cases the third-person possessives lose the -j-.
Who could say that Whose is tthe big armchair is wrong,it it is an exact translatkion from English