OK, since nobody else has stepped up, I'll give it a shot.
First off, I personally would not put my kids in a TT. There is just not enough room for it to be safe. As you said, you have to put one up front which is not as safe, even without the airbag. Secondly, the back seat of that car can barely fit a purse, let alone a carseat (I have been in one, it's TINY). The lack of space means an increase risk of them hitting the interior in a crash. Also, the shear PITB factor of trying to get them in there would be enough to put me over the edge.
Given all that. I would say put the rear-facing Roundabout up front, airbag OFF, seat pushed forward until it is braced on the dashboard and tether it if possible. In the back, try a Radian. It is narrow with a small bottom and may fit down in the seat. If the Radian won't sit down in the seat or install well, then something like a Roundabout may work with the small base down in the scoop of the seat. Top tether if available.
The techs can chime in here with their thoughts, but that is my best guess today.
Mama to three boys ('03, '05, '07)