CSS Loading before bootstrap in child theme

Hello,

I’m trying to use a child theme. So far I’ve been using this as reference to make it: https://codex.wordpress.org/Child_Themes

The main issue is that, if I install the queue in functions.php, as

<?php
function my_theme_enqueue_styles() {

    $parent_style = 'parent-style'; // This is 'twentyfifteen-style' for the Twenty Fifteen theme.

    wp_enqueue_style( $parent_style, get_template_directory_uri() . '/style.css' );
    wp_enqueue_style( 'child-style',
        get_stylesheet_directory_uri() . '/style.css',
        array( $parent_style ),
        wp_get_theme()->get('Version')
    );
}
add_action( 'wp_enqueue_scripts', 'my_theme_enqueue_styles' );
?>

This causes the CSS load order to be:

theme css
child theme css
bootstrap css

which of course is an issue. The right order should be:

bootstrap
theme css
child theme css

How can I do this?

Also, I read in other posts that you can only change the WordPress files, not the ones in the /inc folder. If I want to change those files, what’s the best way to go around?

Thanks!