Well, DH can't drive with a rfing seat behind him. So in his car, DD1 will be in her booster behind him. DD3 will be in the infant seat in the middle, and DD2 will be rfing behind the passenger. We still need to test this out and make sure it fits. Right now we have DD1 behind the driver and DD2 behind the passenger.
In our minivan we have bucket seats in the middle and a full bench in the back. I'm the primary driver if it's just me and the kids, but DH drives it if we go somewhere as a family. Ideally, we'll put the two rfing seats in the middle with DD1 in the back. I'm not sure we'll be able to get a rfing seat behind DH, so we might end up with DD2 rfing behind the passenger, DD3 rfing in the middle back row, and DD1 in the booster next to her.