Convertible Car Seat Questions

So we are about to go from infant seats to convertible seats in my 2010. We have used Chicco keyfit 30's for the past year with my twins and they have allowed me to drive semi-comfortably.

Can any of you with two, rear facing car seats currently installed in a Gen III Prius give me feedback on what fits best? If you have two car seats installed, is there room for a small person to fit inbetween with the seats you have? There are so many on the market to choose from and many seem to have similar dimensions.

 

Just as a reference I am 6'1" and my wife is 5'1", hence the backseat question.