ad 5) Victoria has not 5 reigning monarchs but 6 kings and 1 granduke unlike Christian IX who has 6 in total:
Victoria: Elizabeth II, Harald V, Carl XVI Gustav, Margrethe II, Philippe, Henri, Felipe V
Christian IX: Margrethe II, Harald V, Elizabeth II, Felipe V, Philippe, Henri
ad 6) Queen Emma of the Netherlands herself descended from George II through his oldest daughter Anne, Princess Royal and Princess of Orange as well as through his oldest son Frederick Prince of Wales.
George II - Frederick - Augusta Duchess of Brunswick - Augusta Duchess of Wurtemberg - Paul prince of Wurtemberg - Pauline Duchess of Nassau-Weimar - Helene princess of Waldeck-Pyrmont - Emma Queen of the Netherlands
George II - Anne - Caroline duchess of Nassau-Weimar - William duke of Nassau-Weimar - Helene princess of Waldeck-Pyrmont - Emma Queen of the Netherlands.
The King of the Netherlands is not Willem IV. He is King Willem-Alexander I. He will not use a post-nominal numeral until there is Willem-Alexander II making the number necessary.
Please correct any factual errors, but I wanted to get a clear picture of the relationships amongst the reigning European royals today:
1) He's a direct ancestor to eight of the ten remaining hereditary monarchs of Europe today -- the seven kings (for practical reasons, I count Their Majesties Elizabeth II of Great Britain and Margrethe II of Denmark as "kings") and one grand duke.
2) The three Benelux sovereigns descend from him but not specifically from Queen Victoria (a great-great-grandchild of his).
3) However, two of those three do descend from King Christian IX of Denmark (another great-great-grandchild of his: yes, the "Grandmama of Europe" and "Father-in-law of Europe" were third cousins) -- just like four of the five kings who descend from Victoria.
4) Those two also descend from King Leopold I of the Belgians, who was not only a maternal uncle of Victoria but also, a paternal uncle of her first cousin and husband, Albert.
5) The king of Sweden descends from Victoria but not Christian IX -- just like the abdicated King Juan Carlos of Spain. Thanks to Queen Sofia, Christian IX (since the accession in 2014 of King Felipe VI) has six descendants sitting on thrones today, which is one up from Victoria ("only" five).
6) Willem IV of the Netherlands is the only king who does not descend from either Victoria or Christian IX. He does, however, descend from George II (their mutual great-great-grandfather) through at least two lines: his daughter Anne (the Princess Royal) married Prince Willem IV of Orange and became a direct patrilineal ancestor of Queen Wilhelmina; his son Frederick (Prince of Wales) was an ancestor of Princess Emma of Waldeck and Pyrmont, who became the second queen consort of King Willem III and mother of Queen Wilhelmina.
7) The Dutch king certainly is not the only reigning European monarch not directly descended from Victoria of Christian IX, since this also characterizes the sovereign princes of Monaco and Liechtenstein. However, the latter will eventually be added to the list of George II descendants sitting on thrones, once Prince Joseph Wenzel succeeds. Ironically, the future sovereign of this principality descends from the Protestant British king (who succeeded to the throne as the heir-general of the Electress Sophia of Hanover, thanks to the 1701 Act of Settlement) through his mother, the future Jacobite pretender.
Is all this true? It's interesting to note that with the eventual accession of Prince Joseph Wenzel to the throne of Liechtenstein, Monaco will be the only reigning monarchy headed by a sovereign not descended from King George II of Great Britain. The only way for this tiny principality to join the list would be, if by some fluke, Princess Alexandra of Hanover (who converted to Roman Catholicism some time ago) sat on the throne one day as the reigning princess.