The eldest male member of his family of his generation, Pietro was proclaimed heir to the position of Grand Master by Andrea when Andrea was on his deathbed in 1580, "by reason of primogeniture". Pietro accession to the position in that year, and his own eventual proclamation of his eldest son, Giovanni Andrea I, as his heir, cemented the position of Grand Master as being hereditary.[4] Giovanni Andrea was born on 20 March 1569. Pietro and his wife, Lucrezia Beolchi, also had a second son, Giacomo Antonio, who died before Giovanni Andrea.[9] Pietro's last will, signed on his deathbed on either 29 or 30 July 1592, specified that in the event of the extinction of his own descendants, the Grand Mastership should pass to Michele, son of Pietro's uncle Girolamo I, who was co-Grand Master until 1591. Michele's branch of the family eventually succeeded to the position given that Pietro's sons were childless.[10]
Pietro also had an adopted son, Giovanni Battista Gilio (attested in Latin in a 1602 document as "Ioannes Baptista Gilius Angelos Flavius Firmanos"), who was willed a portrait by an unknown artist from Bologna upon Pietro's death. Giovanni Battista continued to play a role in the Constantinian Order and the Angelo Flavio Comneno family after Pietro's death, verifying the succession of Giovanni Andrea I and later serving as the order's grand chancellor.[10]
Underlined individuals officially claimed the style "Emperor of Constantinople", or equivalent Individuals marked with ‡ have relatives/"successors" maintaining their claims