Wondering if you found further info on this couple. I found six children for their son Joost and am developing their lines but did not have their son Jan or any others.
We know Joost and Martina Westin had more children as Joost Jr. writes from NY back to his sibilings in perhaps Holland?
From "New Harlem, Past and Present" by Carl Pierce is the following indicating where Joost, Sr.'s other children ended up.
"The parents soon returned to Europe leaving young Joost in Harlem as indicated in a letter, written soon after the English took New York, to his virtuous, well beloved brothers and sisters, reading: "Know, my beloved brothers that we are here in the land before this called New Netherland, and now New England by the English masters, being to the injury of our Dutch nation,"