Capability to edit own posts and not others

The capabilities that you are trying to restrict are

• delete_others_posts
• edit_others_posts

Apart from Super Admin and Administrator, the only Role that have these permission is Editor. So, removing these capabilities from Editor should accomplish this.

/**
 * Remove capabilities from editors.
 *
 * Call the function when your plugin/theme is activated.
 */
function wpcodex_set_capabilities() {

    // Get the role object.
    $editor = get_role( 'editor' );

    // A list of capabilities to remove from editors.
    $caps = array(
        'delete_others_posts',
        'edit_others_posts',
    );

    foreach ( $caps as $cap ) {

        // Remove the capability.
        $editor->remove_cap( $cap );
    }
}
add_action( 'init', 'wpcodex_set_capabilities' );

You should only run this code during a plugin or theme activation. From Codex

Note: This setting is saved to the database (in table wp_options, field ‘wp_user_roles’), so you should run this only once, on theme/plugin activation and/or deactivation.