It may be possible to confirm family relationships by comparing test results with Brian 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 37 markers, haplogroup T-M70, FTDNA kit #N239867
Mitochondrial DNA test-takers in the direct maternal line:
Family Tree DNA mtDNA Test Full Sequence, haplogroup J1b1a1-T146C, FTDNA kit #N239867
It is likely that these autosomal DNA test-takers will share some percentage of DNA with Brian: