Ytje Koster, born circa 1850 (?).

Ytje was married to
Sipke van der Zee, born circa 1846 (?), shipwright.

• 1 : Elisabeth van der Zee, born in Harlingen on December 8, 1873.
  Elisabeth was married in Harlingen on December 17, 1894, at the age of 21 to Harmen Gonggrijp (aged 21 years), born in Harlingen on August 7, 1873, son of N.N. and Berbora Gonggrijp (maid servant), blacksmith at the salt works and blacksmith.