This is the route description (included the 75 mile option description b/c the century is that plus some):

75 Miles/Three State Challenge: An exhilarating and challenging ride through three states. A loop east through Connecticut, north into Massachusetts, and west back to Copake Falls, New York, before the return to Millerton. Riders climb through Mt. Washington Forest in southern Massachusetts and are rewarded with a breathtaking descent into New York. Includes some especially hilly and demanding terrain. Cumulative elevation gain: 5,590 feet.

100 Miles/Three State Century: Same as the 75-mile ride plus an additional 25-mile loop south and east to Kent, Connecticut. A long and challenging ride with some mountainous terrain. Cumulative elevation gain: 8,105 feet.
How much climbing-specific training will I have to do for that? There is a great 30-mile hill climb loop near where I live, over a mountain, that I hope to include on my weekend rides but I probably can't do those kinds of hills on weekdays. I also try to really challenge myself on climbs in spin class, pushing the resistance and doing seated climbs.

I might be able to do back to back long rides on some weekends, but certainly not all. DH is training as well, so we will either be taking turns riding and watching the kids, or finding childcare for our weekend rides. Add in the kids' swim lessons, soccer practice, playdates, birthday parties, and, well, you get the gist.

I'm wondering if I am setting my sights too high, and if I should just do the 55 or 75 mile route instead at the same event, but I can't bring myself to give up on the hope/desire to do the century.