JSFiddle - React, Tailwind, and code Playground

HTML

<form method="post">
<div id = "f1">
    <div class="label">Value 1:</div>
        <input type="text" name="name"/>
        <input type="text" name="name"/>
        <input type="text" name="name"/>
        <button id = "next1" type="button" class="check-btn">Next</button>
    </div>
<div id ="f2">
    <div class="label">Value 2:</div><br>
        <input type="text" name="name"/>
        <button type="button" class="check-btn">Next</button><br/>
    </div>
<div id ="f3">
    <div class="label">Value 3:</div><br/>
        <input type="text" name="name"/>
        <input type="text" name="name"/>
        <input type="text" name="name"/>
        <input type="text" name="name"/>
        <input type="text" name="name"/>
        <button type="button" class="check-btn">Next</button><br/>
    </div>
</div>
</form>

JavaScript

$(document).ready(function(){
    $('.check-btn').on('click',function(){
        var parent = $(this).parent('div');
        var elems = parent.find('input');
        alert(elems.length);
        //DO checks here for each element
    });
});