It may be possible to confirm family relationships by comparing test results with Pierre 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 R-M269, FTDNA kit #IN24547
Mitochondrial DNA test-takers in the direct maternal line:
Family Tree DNA mtDNA Test Full Sequence, haplogroup T1A1, FTDNA kit #IN2454
It is likely that these autosomal DNA test-takers will share some percentage of DNA with Pierre:
AncestryDNA, GEDmatch A094727[compare], Ancestry member pssavage45