StephenH

Just about anything is possible on the bike. Actually finding it at the price you care to pay may not be so possible, though. You can build a bike for that geometry, but finding a used one would be a challenge.
Generally, you'll find frames in the "large", "medium", "small" and "large front/ small rear" combinations. Try checking into the "medium" frames and see how close you each can be fitted there.
One stoker I rode with said she could only ride with tall captains because the height of the captain's seat also limits how high the stoker handlebars can be mounted (and she had back issues). There's likely some way around that, but still, a factor to keep in mind that may not be obvious.
When I bought my CoMotion Primera several years ago, for an extra $500, you could get custom geometry. The Primera was their low-end model. I don't know what the limits are on the custom geometry, or what your budget is, but that's something to look into perhaps.
The CoMotion Periscope is set up specifically to accommodate a large range of riders, basically, when your kid is the stoker and is growing, so you don't have to keep buying new bikes. But, check into the geometry ranges on one of them, it may cover a wider range than standard frames. They do show up on the used marked on occasion.
There is a Bilenky tandem with stoker in front in a recumbent-seat, captain in back upright. I've never used one, but that might be an option. I have seen used ones for sale once or twice and they weren't going for that much due to the odd configuration.
They do make recumbent tandems if that is of interest.
There are several tandem-specific dealers around the country, and if one of them is in your area, a visit or an email might be very informative.
A minor issue, but note that a shorter stoker gives you a better view through a mirror. (Of course, the shorter stoker has less of a view ahead, too!)