Prince William invited his cousins to a Royal Family party “via WhatsApp”, royal sources have claimed. Peter Phillips, Zara Tindall, Princess Beatrice, and Princess Eugenie all accompanied their cousin, the Prince of Wales, to a Buckingham Palace garden party earlier this week. Almost all 8,000 guests received their invitations through the post, on thick, cream cards with embossed letters. However, according to sources in The Telegraph, the Prince of Wales sent his four cousins plus Mike Tindall a WhatsApp message to invite them to the garden party. Peter Phillips, Zara and Mike Tindall, Princ…