His Croatian Serb father Milivoj was a military officer in the Austrian army in Lika (a region in today's Croatia), and his mother Vilma was born to Jewish parents from Osijek, Julius and Charlotta (née Weiss) Miskolczy.

[10] Marriage between Branko, and his first wife, Edith dissolved in a series of affairs, and he married his Japanese language translator, Yoshiko Yamasaki.

The ring leader sought advice from the Centre in Moscow, but the instructions were that Vukelić should stay in Japan and continue working for the network.

Vukelić's success in his task resulted in a July 1, 1939 New York Herald Tribune article titled "Japan Believed Still Aiming at South Sea Area", written by Newman.

Their son Hiroshi Yamasaki Vukelić lives in Japan and Belgrade today and works on Japanese-Serbian relations.