Filtering google fonts

I’m trying to filter the fonts displaying in the typography field. The following code shows the correct choices in the dropdown, but selecting them does not load the font.

	$fields[] = array(
		'type'        => 'typography',
		'settings'    => 'font_body',
		'label'       => esc_attr__( 'Body Font', 'sage' ),
		'section'     => 'typography_general',
		'default'     => array(
			'font-family'    => 'PT Serif',
			'line-height'    => '1.8',
			'variant'        => 'regular',
			'font-size'		 => '16px',
			'letter-spacing' => '0',
			'subsets'        => array( 'latin-ext' ),
		),
		'choices'  => array(
			'fonts' => array(
				'google' => array('Lato', 'Playfair Display', 'PT Serif'),
			),
		),
		'priority'    => 10,
		'output'      => array(
			array(
				'element' => 'body',
			),
		),
		'transport'   => 'auto',
	);

Secondly, is it possible to add custom fonts to the typography dropdown (e.g. from fontsquirrel) or will I be better off using the select field?

Thanks