1. There's always a triplizer middle ring if one would survive on a tandem. Might even work with the current cranks set. Wouldn't be hard to get one made if not. I know a guy who could if you can't find one that survives on a tandem, assuming there's no other clearance issue.
2. We cheated by having a da Vinci tandem, so I just changed the middle ratio. Instead of a 34->17 in the middle it's 34->22. Add a (I think) 34 on the back with the 12 on the front and 26" wheels and we're at about 13 gear inches on the low end, and some days it feels like not enough with some of the hills around here. I wouldn't normally let a random pair of strangers ride our bike, but seeing as you've ridden a tandem more on one trip than I do in a year you're welcome to try it out if you want to see how that ratio feels. If your location is correct you also live within about 3 miles of me as the crow flies, so it wouldn't be hard to arrange.