Hi and welcome!
I don't have first hand experience with a Camry, but you could check out the Successful 3 Accross thread and then click "search this thread" at the top right to look for your car. Here is the link:
http://car-seat.org/showthread.php?t=33226&highlight=successful
Is your two year old currently rear facing or forward facing? What seat is he or she using now?
The Camry is a big enough car. I am confident that it is 100% doable.
Are you planning on getting infant seats or convertibles for the twins?
If it was me, I would be buying two Graco Safeseats (go to 30 lbs and about a year) and putting a Radian in the middle seat. But if your two year old is still rear-facing, it's possible the Radian would be too tall for the Camry (would hit the back of the front seats). It might not, though. Often rear-facing Radians fit between the front seats and it's a non-issue. You would have to try it out first, though.
The Safeseats would be nice because they have built-in lockoffs, so you won't have to bother with locking clips. The Radian would be nice because it's super narrow and will fit a child up to 5 or 6 yrs old. Also, when the time comes to move the twins to convertibles, the Radian would still be narrow enough to fit between two bigger seats (ie two Marathons, which is also what I would buy
).
But hopefully someone with a Camry can chime in!
Congratulations btw!