Ellen,
It certainly looks like Pieter was a brother of Jonas:
Probable marriage of Pieter, Amsterdam 7 October 1645:
Index record:
registration date: 07-10-1645 (7 October 1645)
name of groom: Bronck, Pieter Jonas
name of groom: Jonaszon, Pieter
name of bride: Jans, Hilletje
source reference: DTB 462, p.321
comments: Huwelijksintekeningen van de KERK.
Image of bann (right page, top entry):
"Netherlands, Noord-Holland Province, Church Records, 1523-1948," images, FamilySearch (https://familysearch.org/pal:/MM9.3.1/TH-1961-31144-7504-17?cc=2037985 : 21 August 2014), Nederlands Hervormde > Amsterdam > Huwelijksaangiften, Trouwen 1644-1645 > image 388 of 469; Nederlands Rijksarchiefdienst, Den Haag (Netherlands National Archives, The Hague).
Information from bann:
Pieter age 28 years
Hilletje age 20 years
Maybe a daughter of Pieter, Amsterdam 12 August 1646:
Index record:
child: Marritjen
date of baptism: 12-08-1646
church: Lutherse Kerk
religion: Evangelisch-Luthers
father: Bronck, Pieter
reference: DTB 141, p.362
Image of baptism registration (left page, first entry dated 12):
"Netherlands, Noord-Holland Province, Church Records, 1523-1948," images, FamilySearch (https://familysearch.org/pal:/MM9.3.1/TH-1961-31163-10609-15?cc=2037985 : 21 August 2014), Evangelisch Luthers > Amsterdam > Dopen 1641-1656 > image 189 of 650; Nederlands Rijksarchiefdienst, Den Haag (Netherlands National Archives, The Hague).