How to validate checkbox in java script

I'm trying validate checkbox in my java script,but always doesn't work.

what's wrong in the code below:

Html

 <div class="form-group id=Knows">
 <input type="checkbox" name="Knows1" id="Knows1" value="Knows1">Knows1
 <input type="checkbox" name="Knows2" id="Knows2" value="Knows2">Knows2
 <input type="checkbox" name="Knows3" id="Knows3" value="Knows3">Knows3
 <input type="checkbox" name="Knows4" id="Knows4" value="Knows4">Knows4 
 <input type="checkbox" name="Knows5" id="Knows5" value="Knows5">Knows5
 </div>

Java script

 parent_fieldset.find('#Knows1, #Knows2, #Knows3, #knows4').each(function() {
 if( $(this).checked == "false" && $("#Knows5").checked =="false") {
 $(this).addClass('input-error');
 next_step = false;
 }
 else {
 $(this).removeClass('input-error');
 }
 });