Ok, taking all that into consideration, I would probably put the Marathon and the Maestro in car #2 (assuming it's fine if both seats are outboard in that car, because they're definitely not going to fit side by side unless it's a huge car), and then get two new seats for car #1.
For your 3 year old, the Graco Nautilus or the Britax Frontier. The Frontier harnesses longer, and has a lot of nice little features that the Nautilus doesn't, but is quite a bit more expensive.
For the baby, I would lean heavily towards the Radian because I know it'll fit next to either seat and still leave room for a passenger on the other side and it has all the ERF capabilities you want. Technically, they do need to be 12 months to use the angle adjuster, but the engineers have said that was just them being cautious to be sure no one used it with a young baby without head control. I would be fine using it with a 9-10 month old.
Also, with a Radian and a Frontier they could easily be almost last seats you buy... the Frontier has a 9 year expiration, and the Radian has nice high top slots so theoretically, your 3 year old could use the Frontier in harness mode for the next 4 years, when he'll be 7 and could switch to booster mode if you want to, leave #2 in the Radian until she's outgrown it in height, probably another 2 years past that at which she'll be 6 and your oldest will be 9, move her into the Frontier in booster mode and him into a backless booster and you're set. So it's a pretty decent investment.
And I totally feel your pain about the Marathon sitting up so high lol personally I've always disliked that!