<div class="row mb-2">
    <div class="col-lg-3 col-md-12">
      <a href="<?php echo $host; ?>" title="<?php echo html($site_config['logo_text']); ?> - <?php echo html($site_config['logo_slogen']); ?>" class="header_logo_to_link">
            <img src="<?php echo $host; ?>/images/assets/logo_33.png" alt="<?php echo html($site_config['logo_text']); ?> - <?php echo html($site_config['logo_slogen']); ?>" class="img-responsive footer_logo_image" />
        </a>
    </div>
    <div class="col-lg-6 col-md-12">
       <form id="FooterNewsletterForm" method="post">
            <h4 class="footer_title">Feliratkozás a hírlevélre</h4>
            <div class="row">
                <div class="col-6 mb-3">
                    <input type="text" class="form-control footer_newsletter_input" placeholder="Név" name="NewsletterVname" id="NewsletterVname" />
                </div>
                <div class="col-6 mb-3 input-group">
                    <input type="text" class="form-control footer_newsletter_input" placeholder="E-mail cím" name="NewsletterEmail" id="NewsletterEmail" />
                    <div class="input-group-append">
                        <button class="btn btn-default footer_newsletter_button" id="NewsletterButton" name="NewsletterButton" type="submit">Feliratkozás</button>
                    </div>
                </div>
                <div class="clearfix"></div>
            </div>
            <div class="checkbox checkbox_allow_div mb-2 custom-control custom-checkbox">
                <input type="checkbox" name="allow" id="nws_accept" value="1" class="allow_checkbox custom-control-input">
                <label class="label_300 custom-control-label" id="nws_accept_label" for="nws_accept"><?php echo gdpr_text('gdpr_newsletter_text'); ?></label>
            </div>
        </form>
    </div> 
    <div class="col-lg-3 col-md-12">
        <h4 class="footer_title">Közösségi oldalaink</h4>
        <h4 class="footer_title">Közösségi oldalaink</h4>
        <?php
        if($site_config['k_fb'] != "" )
        {
            echo '<div class="footer_social_divs float-left mr-3">
                    <a href="'.html($site_config['k_fb']).'" title="Facebook" target="_blank"><i class="fab fa-facebook-square" aria-hidden="true"></i></a>
                 </div>';
        }
        if($site_config['k_twitter'] != "" )
        {
            echo '<div class="footer_social_divs float-left mr-3">
                    <a href="'.html($site_config['k_twitter']).'" title="Twitter" target="_blank"><i class="fab fa-twitter-square" aria-hidden="true"></i></a>
                 </div>';
        }
        if($site_config['k_youtube'] != "" )
        {
            echo '<div class="footer_social_divs float-left mr-3">
                    <a href="'.html($site_config['k_youtube']).'" title="Youtube" target="_blank"><i class="fab fa-youtube-square" aria-hidden="true"></i></a>
                 </div>';
        }
        if($site_config['k_instagram'] != "" )
        {
            echo '<div class="footer_social_divs float-left">
                    <a href="'.html($site_config['k_instagram']).'" title="Instagram" target="_blank"><i class="fab fa-instagram" aria-hidden="true"></i></a>
                 </div>';
        }
        ?>
    </div>
    <div class="clearfix"></div>
</div>

In a .container-fluid div, i have this html code:

<div class="row mb-2">
        <div class="col-md-3">
            <a href="<?php echo $host; ?>" title="<?php echo html($site_config['logo_text']); ?> - <?php echo html($site_config['logo_slogen']); ?>" class="header_logo_to_link">
                <img src="<?php echo $host; ?>/images/assets/logo_33.png" alt="<?php echo html($site_config['logo_text']); ?> - <?php echo html($site_config['logo_slogen']); ?>" class="img-responsive footer_logo_image" />
            </a>
        </div>
        <div class="col-md-6">
            <form id="FooterNewsletterForm" method="post">
                <h4 class="footer_title">Feliratkozás a hírlevélre</h4>
                <div class="row">
                    <div class="col-6 mb-3">
                        <input type="text" class="form-control footer_newsletter_input" placeholder="Név" name="NewsletterVname" id="NewsletterVname" />
                    </div>
                    <div class="col-6 mb-3 input-group">
                        <input type="text" class="form-control footer_newsletter_input" placeholder="E-mail cím" name="NewsletterEmail" id="NewsletterEmail" />
                        <div class="input-group-append">
                            <button class="btn btn-default footer_newsletter_button" id="NewsletterButton" name="NewsletterButton" type="submit">Feliratkozás</button>
                        </div>
                    </div>
                    <div class="clearfix"></div>
                </div>
                <div class="checkbox checkbox_allow_div mb-2 custom-control custom-checkbox">
                    <input type="checkbox" name="allow" id="nws_accept" value="1" class="allow_checkbox custom-control-input">
                    <label class="label_300 custom-control-label" id="nws_accept_label" for="nws_accept"><?php echo gdpr_text('gdpr_newsletter_text'); ?></label>
                </div>
            </form>
        </div> 
        <div class="col-sm-12 col-md-3">
            <h4 class="footer_title">Közösségi oldalaink</h4>
            <?php
            if($site_config['k_fb'] != "" )
            {
                echo '<div class="footer_social_divs float-left mr-3">
                        <a href="'.html($site_config['k_fb']).'" title="Facebook" target="_blank"><i class="fab fa-facebook-square" aria-hidden="true"></i></a>
                     </div>';
            }
            if($site_config['k_twitter'] != "" )
            {
                echo '<div class="footer_social_divs float-left mr-3">
                        <a href="'.html($site_config['k_twitter']).'" title="Twitter" target="_blank"><i class="fab fa-twitter-square" aria-hidden="true"></i></a>
                     </div>';
            }
            if($site_config['k_youtube'] != "" )
            {
                echo '<div class="footer_social_divs float-left mr-3">
                        <a href="'.html($site_config['k_youtube']).'" title="Youtube" target="_blank"><i class="fab fa-youtube-square" aria-hidden="true"></i></a>
                     </div>';
            }
            if($site_config['k_instagram'] != "" )
            {
                echo '<div class="footer_social_divs float-left">
                        <a href="'.html($site_config['k_instagram']).'" title="Instagram" target="_blank"><i class="fab fa-instagram" aria-hidden="true"></i></a>
                     </div>';
            }
            ?>
        </div>
        <div class="clearfix"></div>
    </div>

On large screens, the display is okay, but on mobile devices, the div what has the form inside it, it goes wrong, as you can see it on the uploaded picture, and also, the input group is showned wrong.

Link to my demo site:

On mobile devices, i want those 3 divs under each other. For this, i tryed col-sm-12, col12, but nothing, it was still the same problem.