Hi! What a surprise. I just found out that one of my Grandfather John Heidenfelder's brothers was also a Stefan Heidenfelder, another was Robert (he was a Roman Catholic priest).

So,
1. Stefan Heidenfelder ---- my grandfather's brother it seems -- born before or after his birthdate of 1891.
2. Stefan Heidenfelder ---who seems to be a son of the above (that would explain why my Father called this one his 1st cousin)...yikes!... was born Sept 22, 1902 -- In Nakovo, Banat, Yugoslavia, died Oct 9 1978 in Aurora, Denver, Colorado, USA. He married Helen Merle (in Nakovo) and had three children.

I hope this is a connection, as I have been looking for decades. Look forward to hearing from you again.