Bos

Nobody did help me, so after a long time of trial and error I solved this problem myself.
Every hiding that has to fullfill to the same condition you have to write an if/else statement more with another hide number.
Every other hide condition you have to write a new JQuery script. See step 3 of the work of BunnyBomb.
You have to give this script another filename. For instance hidefieldsScript2.js.
Ad this file directly into the “js” folder for your theme (example: “./wordpress/wp-content/themes/your-theme-name/js/”.
Don’t forget step 5 by adding “<script type=”text/javascript” src=”<?php echo get_stylesheet_directory_uri(); ?>/js/hidefieldsScript2.js”></script> to the header.php
Now you are able to expand the contact form with extra hidings and new conditions for hiding.
It works great!

Second hiding doesnot show up?
The first hidefunction operates perfect, I added e second hide function (and i am intending to create more hidefunctions). But the field doesnot show up?
See the jQuery code and the contactform code here below. What i am doing wrong?

[ Moderator Note: Please post code or markup snippets between backticks or use the code button. ]

/*! jQuery script to hide certain form fields */
$(document).ready(function() {
	//Hide the field initially
	$("#hide1").hide();
  $("#hide2").hide();
	$("#hide3").hide();
	//First hidefunction: Laat de tekst zien, waneer resp "ik kom niet", "mijn partner komt niet" gekozen wordt.
	$('#wieniet').change(function() {
		if ($("#wieniet").val() == "ik kom niet") {
			$("#hide1").show();
		}
		else {
			$("#hide1").hide();
			}
			if ($("#wieniet").val() == "mijn partner komt niet") {
			$("#hide2").show();
		}
		else {
			$("#hide2").hide();
			}
	});
//Second hidefunction:Laat de tekst zien, waneer resp "graag informatie over mogelijke invaller", "ik zorg zelf voor een invaller" gekozen wordt.
	$('#intinv').change(function() {
		if ($("#intinv").val() == "ja") {
			$("#hide3").show();
		}
		else {
			$("#hide3").hide();
			}
  });
});

Contact Form 7 code:
<table>
<tr>

<td><label for="wieniet">Wie komt er niet?*</label></td>
<td>[select* wieniet 20 id:wieniet include_blank class:contactForm "ik kom niet" "mijn partner komt niet" "mijn partner en ik komen niet"]</td>
<tr>
<td><div class="hide" id="hide1">
        <label for="telp">Telefoonnr. partner*</label>
        [text* telp 11/11 id:telp class:contactForm]

 <label for="intinv">Interesse om met invaller te spelen?*</label>
[select* intinv include_blank "ja" "nee"]
</div>

<div class="hide" id="hide2">
          <label for="mtel">Mijn telefoonnr.*</label>
          [text* mtel 11/11 id:mtel class:contactForm]
  <label for="intinv">Interesse om met invaller te spelen?*</label>
[select* intinv include_blank "ja" "nee"]
</div>

</tr>
<tr>
<td>
<div class="hide" id="hide3">

  <label for="zinv">Indien er interesse is om met een invaller te spelen:*</label>
[select* zinv  id:intinv include_blank class:contactForm "graag informatie over mogelijke invaller" "ik zorg zelf voor een invaller"]
</div>
</td>
</table>