Pieter was from the Hollegraeff family, which was well-established in the Blokzijl district. Their baptisms and marriages may be traced through the Blokzijl books, but, unfortunately, Pieter's marriage to Brechje Mollerus has not been found. The Blokzijl marriage books for the period 1660-1684 do not exist anymore. As it is, they baptise their first child, Treintje, in Amsterdam's Nieuwe Kerk in 1687. However, their marriage cannot be traced in the books of that parish either.
When the banns for the marriage of Brechje Mollerus to Joen Pieter Booyens are announced on 26 August 1694, her name is entered in the books of the Blokjizl church as "the widow of Pieter Hollegraaff".