If your family was Roman Catholic, their church records will be in Latin. These records used the Latin version of names. Since Dutch search engines only find exact matches, you will need to search for these Latin names or use wildcards.
For example, my ancestor Jan Smulders appeared in Catholic records as Joannes. His father Hendrik is called Henricus in Latin. Searching for “Jan Smulders” would not have found his baptismal record, but J* Smulders would have. Even initials can change though; a woman named Anneken may have been known in Catholic records as Joanna.