If this is what your html looks like, then jQuery(element).siblings("label")
selects all labels, because they are all contained in the same element and are thus siblings with eachother. To prevent this, you should put all label+input pairs in to their own element, like so
<div>
<label id="jform_first_name-lbl" for="jform_first_name" class="hasTooltip required" title="">First name<span class="star"> *</span></label>
<input type="text" name="jform[first_name]" id="jform_first_name" value="" class="fild {rules:{required:true}}" size="30" required aria-required="true" />
</div>
<div>
<label id="jform_surname-lbl" for="jform_surname" class="hasTooltip required" title="">Surname<span class="star"> *</span></label>
<input type="text" name="jform[surname]" id="jform_surname" value="" class="fild {rules:{required:true}}" size="30" required aria-required="true" />
</div>
<div>
<label id="jform_mobile-lbl" for="jform_mobile" class="hasTooltip required" title="">Mobile<span class="star"> *</span></label>
<input type="text" name="jform[mobile]" id="jform_mobile" value="" class="numeric fild {rules:{required:true}}" size="30" required aria-required="true" />
</div>
Alternatively you can change siblings
to https://api.jquery.com/prev/