(1) He is married to (Not public).
They got married
(2) He is married to Pieternella Sijncke.
Permission for the marriage has been obtained in Kruiningen on May 22, 1778.Source 1
1157. Otr. 22 mei, Jan Janse Haverhoek, laatst wr. van wijlen Maria Krijnse, wonende te Hoedekenskerke, met Pieternella Sijncke, jd. geboren en wonende alhier.
Kruiningen index ref. trouwen 1671-1810 https://geneaknowhow.net/script/zee/Trouwen%20Kruiningen%201671-1810.pdf