If you go to www.car-seat.org you can post your question (and list the year of your CRV and and the ages/weight/height of all children and you'll get all the info you'll ever need. They are the most helpful folks over there and they will direct you toward the best choices, not always the most expensive seats either, but the one's that will work best for you and your children.
Please do not as as someone suggested put your oldest in a booster at 3, it is way too early, children are much much safer in a 5pt harness until age 5. I know that using the seatbelts rather than latch allows some extra room, but it will really depend on the seats you get, but again the folks at car-seat.org have got all the info you could need and the expertise in which seat configuration works. You also need to take into consideration things like the fact that your 15 month should remain rearfacing until at least 2 or the weight limits of your seat and the baby will be rearfacing for quite a while which will impact seat positioning in the back seat and may require the front seats to be pushed forward (one of the reasons I love my minivan, lots of space to keep my DS rearfacing, he'll be 3 in March, weighs 30 lbs and will remain rearfacing till he's 33 pounds.)