Hi,
I think, that you will have help from;

Pani Halina Ladon
Redaktor "Echo Klucz"
32-310 Klucze
woj.malopolskie
Poland
She is publisher of local newspaper for Gmina Klucze;
http://www.gmina-klucze.pl/index.php?menu_id=36
Chechlo is a vilage in this gmina.
Probably she will be very interested about Stefan's fate
for her "Echo Klucz" and will help you in contact with
Stefan's relatives.

Cordially,
Wladyslaw