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 R2, FTDNA kit #859903
Mitochondrial DNA test-takers in the direct maternal line:
Family Tree DNA mtDNA Test Full Sequence, haplogroup U4a, FTDNA kit #857874
It is likely that these autosomal DNA test-takers will share DNA with Mark: