J.Y.
I highly reccommend you buy a carseat that will keep them rear-facing as long as possible. Research shows that it is the safest way for a baby to ride, even after 1 year old and 20 lbs. If you are in a frontal impact crash the baby's spine can be seriously injured when facing forward because their head is not proportionate to their body. (Look at the site Joel's Journey for a good explanation) My son is 28 months old and still comfortably rides rearfacing. He will move forward facing when he reached the 35 pound weight limit. I can understand your concern about the cost of the seats. You can check with your local police or fire department to see if they give away carseats. When I went to an installation check at my police department the installer was concerned that my 4 year old was not big enough to be forward facing (he has medical problems and was 36 inches tall and only weighed 24 pounds). The carseat I had for him could not be used rear facing so the officer gave me a new carseat. If you can't find a source for a free carseat then any carseat that fits properly in your car and within the weight/height limits of your children is a safe carseat. You don't have to buy the really expensive ones. I think taking them in and out of the car every day will be a huge headache. It isn't easy to install the seat correctly quickly with two babies waiting to go home. Also, even though it is a pain, you should remove their coats when putting them in the carseat. They can't be buckled in tightly enough with their coats on. Either put their coats on them backwards after being buckled or keep a warm blanket in the car for them.