It may be possible to confirm family relationships by comparing test results with Mark or other carriers of his ancestors' Y-chromosome or mitochondrial DNA.
Y-chromosome DNA test-takers in his direct paternal line on WikiTree:
Family Tree DNA Y-DNA Test 111 markers, haplogroup I-Y128944, FTDNA kit #B408386, MitoYDNA ID T12008[compare]
Mitochondrial DNA test-takers in the direct maternal line:
Family Tree DNA mtDNA Test Full Sequence, haplogroup HV0-T195C!, FTDNA kit #B408386, MitoYDNA ID T12002[compare]