While War of Will is descended from the Minnie Hauk branch of Best in Show's family ("Mares on Monday: War of Will Strikes Winning Note for Minnie Hauk," 1/21/2019), Siskin is from the branch of the Best in Show family descended from Minnie Hauk's full sister Monroe, which was discussed in March of last year in connection with Tacitus' victory in the 2019 Lambholm South Tampa Bay Derby (USA-G2) ("Mares on Monday: Tacitus Writes Another Piece of History for Monroe," 3/11/2019). The son of First Defence is in fact closely related to Tacitus' dam Close Hatches, the American champion older female of 2014, who like him is by First Defence out of a daughter of Monroe's stakes-placed daughter Silver Star (by Zafonic).
The difference in the pedigrees of Siskin and Close Hatches is in their broodmare sires. While Close Hatches is out of the Storm Cat mare Rising Tornado (also the dam of Close Hatches' full sister Lockdown, a multiple Grade 1-placed stakes winner), Siskin is the second foal out of the Oasis Dream mare Bird Flown, whose sire is a son of Green Desert and thus represents the Danzig male line. Both the Storm Cat and Danzig male lines have shown plenty of ability to adapt to both dirt and turf, but the sons of Danzig's best sire sons---Danehill and Green Desert---have been almost exclusively European when it comes to their major Northern Hemisphere representatives, giving Siskin's pedigree more of a European slant.
While Close Hatches handled 9 furlongs well, there is little reason to expect that Siskin would want 10 furlongs or more based on pedigree, so the indications by his connections that he is much likelier to target the one-mile Sussex Stakes (USA-G1) at Goodwood than the 12-furlong classics in England or Ireland make perfectly good sense. A first-rate miler is nothing to be sneeze at, either as a racehorse or as a stallion prospect, and even though First Defence is now in Saudi Arabia, the strength of Siskin's female family plus his own obvious quality is reason enough to see whether he proves to be best in show in the stallion barn as well.