Johannes Joost Frits, b2c1 - Mix up between to Johannes Joost Frits and Jan Jurgen Frits

Johannes Joost Frits and Jan Jurgen Frits, I do not think these two are the same person. Looking at the marriage record there is something interesting. Above the entry for Jan Jurgen Frits is the entry for his brother Joseph Johannes David Frits these two married sisters, the Roets girls. Both men are the sons of Joseph Johannes Frits b. 1768 and Albertina Graaf.
The name Jan Jurgen Frits also appears on all the childrens baptisms.

Jan Jurgen Frits was born 2 Feb 1803 and baptized 18 Oct 1807. According to the SA Genealogies GISA book II Page 377 Frits states that he died young, but does not give proof of death. What if they are wrong ?
According to the last child born to Jan Jurgen Frits her baptism states that he is deceased. She, Martha Johanna Elizabeth was born in Oct 1844 and baptized in Oct 1845 . So her father probably died some where in 1845.

Karen