I used a slightly different arrangement when our daughter was young. Similar clamp-on bottom bracket and diagonal chain going to the captain's crank, but I put that chain on the NDS. I then ran a long chain all the way from the captain's crank back to the freewheel on the DS. The normal stoker's crank was removed entirely. Worked fine and eliminated any concerns about cross-chained gears given the length of the drive chain. The crank for my daughter was from a kid's bike and therefore came with short arms. And the chain ring didn't quite match the number of teeth of the cross-over ring on my crank so we were neither in-phase nor out-of-phase, but rather a constantly changing phase. Of course her crank did have the pedals on the 'wrong' side so they tended to unscrew due to precession, but a bit of loctite solved that.
Last edited by prathmann; 04-10-16 at 08:52 PM.