The name Rikkerink is not so common and I have to guess but I think this could be the grandparents of Jack and maybe the son Jacob is the father of Jackhttp://denhaag.digitalestamboom.nl/(emfvl345ptx4iq45kxqa2l45...
Around 1940 / 41 a J. Rikkerink got married with E.C. Schrijvers so maybe this are his parents
The marriage-records of 1940 / 1941 are not public yet.
Maybe you can get hold of the naturalisation papers of Jack ?