How can I run two AJAX requests simultaneously in WordPress?

Kinda stuck here working with AJAX and trying to show posts based on user interaction. Right now I have it working where user makes a category dropdown selection and the posts load accordingly. What I would like to do is take it one step further and populate another drop-down with subcategories based on the parent category that was selected. View the site here.

jQuery

$('#ajaxFilter select').on('change', function(event) {
if(event.preventDefault) { event.preventDefault(); }
$this = $(this);
$value = this.value;
$page = $this.data('page');
$term = $this.data('term');
$qty = $this.closest('#ajaxFilter').data('paged')

    $params = {
        //Bind parameters
        'value': $value,
        'page' : $page,
        'term' : $term,
        'qty'  : $qty,
    };

    //Run the query with those parameters
    get_posts($params);
});



function get_posts($params) {
$content   = $('#ajaxPosts');
$.ajax({
    url: psc.ajax_url,
    data: {
        action: 'filter_posts',
        nonce: psc.nonce,
        params: $params
    },
    type: 'post',
    dataType: 'json',
success: function(data, textStatus, XMLHttpRequest) {
    if (data.status === 200) {
        $content.html(data.content);
    }
    else if (data.status === 201) {
        $content.html(data.message);    
    }
    else {
        $status.html(data.message);
    }
    },
error: function(MLHttpRequest, textStatus, errorThrown) {
    $status.html(textStatus);
     }
});

}

functions.php

function psc_filter_posts() {
if( !isset( $_POST['nonce'] ) || !wp_verify_nonce( $_POST['nonce'], 'psc' ) )
die('Permission denied');

$value = intval($_POST['params']['value']);;
$term = sanitize_text_field($_POST['params']['term']);
$page = intval($_POST['params']['page']);
$qty  = intval($_POST['params']['qty']);

if ( $value == 0 ) : 
    $tax_qry[] = [
        'taxonomy' = 'category',
        'field'    = 'term_id',
        'terms'    = $value,
        'operator' = 'NOT IN'
    ];
else :
    $tax_qry[] = [
        'taxonomy' = 'category',
        'field'    = 'term_id',
        'terms'    = $value,
    ];
 endif;

//Setup the query args for wp query
$args = [
'paged'          = $page,
'post_status'    = 'publish',
'posts_per_page' = $qty,
'tax_query'      = $tax_qry
];

$qry = new WP_Query($args);

ob_start();
if ($qry-have_posts()) : ?
    div class="container"
            ?php while ($qry-have_posts()) : $qry-the_post(); ?

            LOOP STUFF              

            ?php endwhile; ?
    /div!-- .container --

    nav class = "container mt-5 text-center"
        div class="row"
            div class="col-sm-12"
                ?php psc_ajax_pager($qry,$page,$value); ?
            /div!-- .col-sm-12 --
        /div!-- .row --
    /nav

?php $response = [
'status'= 200,
'found' = $qry-found_posts
];
else :
$response = [
    'status'  = 201,
    'message' = 'No posts found'
];

endif;

$response['content'] = ob_get_clean();

die(json_encode($response));

}

add_action('wp_ajax_filter_posts', 'psc_filter_posts');
add_action('wp_ajax_nopriv_filter_posts', 'psc_filter_posts');