google fonts

I see on the forum how to change function.php to add the font ‘catemaran’, but I do not see it show up in my font list. Only if I change register-backend-google-fonts.php what is going wrong. Also I do not see by the existing font Advent Pro the options to choose the 100, 400 or the 600 version.

add_filter( 'avf_google_heading_font', 'avia_add_heading_font');
function avia_add_heading_font($fonts)
{
$fonts['Catamaran'] = 'Catamaran:300,400,800';
return $fonts;
}

add_filter( 'avf_google_content_font', 'avia_add_content_font');
function avia_add_content_font($fonts)
{

$fonts['Catamaran'] = 'Catamaran:300,400,800';
return $fonts;
}