Derk's sister Henriette (Jet, pronounced Yet) Lousie Jansz van der Veer. This is Mariette van der Veer's grandmother. Henriette married Willem Marius van der Veer. They had four children, Bob, Willem (Wim), Heleendert Berend (Bert) and Maria. I did get information that there was possibly another younger daughter as well. Bert is Mariette van der Veer's father, and Maria is Marianne van der Veer Ouwehand's mother.