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 700 markers, haplogroup R-BY98989, FTDNA kit #B258991
It is likely that these autosomal DNA test-takers will share some percentage of DNA with Mark:
AncestryDNA, GEDmatch A266407[compare], Ancestry member MarkAdamsWilliamston