Jan can not be the same person as JanJanssen. JanJanssen dies after 4 years of marriage, so not all of Jan Janmaat's possible children can be his. Maybe Jannes (1713), but there is definitely another Jan Janmaat.
Was Jan Janmaat possibly the father of JannesJanssen? Jannes's father died before 1735, Jan before 1743.
Was Jan Janmaat possibly the father of JudithJanmaat? Judith's father died before 1733, Jan before 1743.
Was Jan Janmaat possibly the father of HarmenJansenJanmaat? No parents mentioned at 1st marriage in 1734, at 2nd marriage he is not surviving son, but the father would be around 90, not probable.
Was Jan Janmaat possibly the father of Janvan hetJanmaat? Jan's father died before 1738, Jan before 1743.
JanJanmaat died b 1743, because he died before Jannes' marriage.1