Since I've sent my two kids chair version, I've changed the setup a little bit. The center of gravity was way too high, and they didn't like the chairs, because it restricted their movements (and they end up behaving worse)
So , I've cut a new snapdeck out of plywood, covered it with a bit of leather and some cushioning, bent some aluminium tubbing - and now they have reasonable security, they don't feel "tied down" and enjoy the trip much more! (it's also much more versatile, since I don't have to carry the two seats around, and the bike is always ready to carry them)
I also upgraded the front end, with a new fork, disc brake, and Alfine dynamo hub powering a B&M IQ Cyo R headlight and Toplight Line rearlight
Cheers,
Miguel B