With the Honda Odyssey though when you put convertible seat in (rear facing or otherwise) where you put it (I think if you put it in the middle, not sure)can mean the cut off of one of the third row of seats because the way it harnesses could cause "decapitation" (it is a legal thing). This how it was explained to me anyway.
Anyhow, I think, in the Odyssey, you could fit a rear facing, your harness booster and a booster in the first row and then the second booster in the back.