Using widget_inits hook and require breaks site

I am trying to unregister and register a new widget class, in order to use a child theme file. However, when I add the action Init_widget, or add the line to require the pathname, the site breaks and I get a server 500 error.

function moesia_child_widgets() {
	if ( function_exists('siteorigin_panels_activate') ) {
		unregister_widget( 'Moesia_Projects' );
		register_widget( 'Moesia_Newprojects' );
	}
}
add_action( 'widgets_init', 'moesia_child_widgets', 99 );
require get_stylesheet_directory() . '/widgets/fp-newprojects.php';

I have my fp-newprojects.php file in moesia-child-01/widget/fp-newprojects.php. I am using the Moesia theme.