1. The current Duke of Grafton, Henry FitzRoy, 12th Duke of Grafton, is a direct descendant of James I and VI of England and Scotland through several lines (including through Charles I and Elizabeth of Bohemia), and through him, of most of English and Scottish Monarchs.
Through a different lineage, the current Duke is also descended from several other English Monarchs, including Edward III (though William Neville, 1st Earl of Kent, a grandson of John of Gaunt, himself the son of Edward III).
Line of descent from James I to Henry FitzRoy, 12th Duke of Grafton:
James I --> Charles I ---> Charles II ---> Henry FitzRoy, 1st Duke of Grafton ---> Charles FitzRoy, 2nd Duke of Grafton ---> Lord Augustus FitzRoy ---> Augustus FitzRoy, 3rd Duke of Grafton ---> George FitzRoy, 4th Duke of Grafton ---> Henry FitzRoy, 5th Duke of Grafton ---> Augustus FitzRoy, 7th Duke of Grafton ---> Lord Charles FitzRoy ---> Charles FitzRoy, 10th Duke of Grafton ---> Hugh FitzRoy, 11th Duke of Grafton ---> James FitzRoy, Earl of Euston ---> Henry FitzRoy, 12th Duke of Grafton
2. The current Duke of Somerset, John Seymour, 19th Duke of Somerset is related by blood to many English Monarchs (among them, Edward VI and the current Monarch - Elizabeth II), however he isn't known to be descended from any of them.
The Dukes of Somerset did have a lot of Royal blood until Algernon Seymour, 7th Duke of Somerset; upon his death, however, the title passed to a distant relative, Edward Seymour, 8th Duke of Somerset (great-great-great-grandson of Sir Edward Seymour, 1st Baronet, himself only son of the 1st Duke’s second son, Sir Edward Seymour). Of course, the Dukes of Somerset still have some of the most illustrious noble ancestry in the Kingdom, not to mention their blood ties to nearly all great noble families of Britain. The current Duke is also related to Queen Elizabeth II through Queen Elizabeth The Queen Mother (born Lady Elizabeth Bowes-Lyon).
3. The current Duke of Norfolk, Edward Fitzalan-Howard, 18th Duke of Norfolk, is a direct descendant of many English and Scottish Monarchs. Among his ancestors are Robert I Bruce, King of Scotland (through Robert I's daughter, Margaret Bruce) and Edward III (through John of Gaunt's son, John de Beaufort, 1st Earl of Somerset).
Line of descent from Edward III to Edward Fitzalan-Howard, 18th Duke of Norfolk
Edward III ---> John of Gaunt ---> John de Beaufort, 1st Earl of Somerset ---> Lady Joan Beaufort ---> John Stewart, 1st Earl of Atholl ---> Lady Elizabeth Stewart ---> Lady Elizabeth Stuart ---> Alexander Gordon, 12th Earl of Sutherland ---> John Gordon, 13th Earl of Sutherland ---> John Gordon, 14th Earl of Sutherland ---> George Gordon, 15th Earl of Sutherland ---> John Gordon, 16th Earl of Sutherland ---> William Gordon, Lord Strathnaver ---> William Gordon, 17th Earl of Sutherland ---> William Gordon, 18th Earl of Sutherland ---> Elizabeth Gordon, Countess of Sutherland ---> Charlotte Sophia Leveson-Gower --->Edward, 1st Baron Howard of Glossop ---> Francis, 2nd Baron Howard of Glossop ---> Bernard, 3rd Baron Howard of Glossop ---> Miles Francis Stapleton Fitzalan-Howard, 17th Duke of Norfolk ---> Edward Fitzalan-Howard, 18th Duke of Norfolk
@ Lady Mary
Genealogy is one of my hobbies and I know the history of most noble families of our country quite well. I would love to read your answer as well though; it would be great to see the answer to this question from a different perspective. :)