It may be possible to confirm family relationships with Unknownfather by comparing test results with other carriers of his Y-chromosome or his mother's mitochondrial DNA.
Y-chromosome DNA test-takers in his direct paternal line on WikiTree:
Max Heffler :
Family Tree DNA Y-DNA Test 111 markers, haplogroup R-Y2630, Ysearch 888HB, FTDNA kit #2805 +
Y-Chromosome Test, haplogroup R-Y2630
Joseph Heffler :
Y-Chromosome Test 48 markers, haplogroup R1a1a*, Ysearch 774DJ
It is likely that these autosomal DNA test-takers will share DNA with Unknownfather: