The Dutch monarchs won't attend. Because the 27th of April (HM birthday) is on a Sunday Kingsday is celebrated on the Saturday the 26th. Because of the Pope's funeral the celebrations of the Royal visit to Doetinchem will start an hour later so they'll be after the funeral in Rome. Neither HM the king nor HM the Queen (a Catholic Argentinian) will attend the funeral. I think the Dutch court messed up on this. It will not cost them much but I believe it would have been possible to postpone the celebrations for several hours in order for TM to attend the funeral and fly back to celebrate Kingsday.
Now the PM and a minister go. At the very least Princess Beatrix, her sister princess Irene (in the eyes of the Catholic church the dowager Duchess of Parma and Piacenza) as well as TRH the count and countess of Bardi could have represented HM the King.