Parents named as Jno. Vankampen and ...iend Larkins.
Marriage brother Cornelis:https://familysearch.org/pal:/MM9.1.1/FCC9-7C9
Parents named as Jno. Vankampen and Bowina Larkens
That brings me to the 1900 census:https://familysearch.org/pal:/MM9.1.1/MS9V-91W
Date of birth of John: Mar 1863, Holland
Date of birth of Bowina: May 1860, Holland
And their marriage:https://familysearch.org/pal:/MM9.1.1/FCYL-V5J
Names are badly transcribed, but is is them.
So now we have a birth month and year for them both.
And that brings me to the following:
Jan van Kampen
Born Westerwijdwerd (province of Groningen) 03 Mar 1863 at 13.00 hrs
Son of Kornelis van Kampen and Jantje Hendriks Kiewiet
Bouke Larkens (female)
Born Bierum (province of Groningen) 16 May 1860 at 22.00 hrs
Daughter of Henderika Larkens, father not mentioned
Do you need to get back further in time?