It may be possible to confirm family relationships by comparing test results with Marvin 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 R-M269, FTDNA kit #446635
Mitochondrial DNA test-takers in the direct maternal line:
Family Tree DNA mtDNA Test HVR1 and HVR2, haplogroup H1a1a1, FTDNA kit #742679
It is likely that these autosomal DNA test-takers will share some percentage of DNA with Marvin: