When Sarah Ferguson became a grandmother to Princess Eugenie’s sons, August, who’s now five, and Ernest, three, she was quick to gush about the arrivals on social media as a proud Granny. But it was a very different story when Eugenie, 36, announced, via Instagram, that she and her husband Jack Brooksbank, 40, had welcomed a baby girl on August 3 in Portugal. In a notable change, the former Duchess of York continued the social media silence she’…