Yes you can as long as they fit in the back seat. In my opinion the evenflo carseats have a smaller base and seat so you could fit three in the back....
just a thought, they should starts making carseats for multiples.....
I think you'd have a hard time trying to fit them all in the back of your elantra. I'd give it a try though. You'd for sure have to get a bigger vehicle once they turn a year old and you switch them to a convertible seat. Best of luck and congrats on the babies!
Like others said you could always give it a try. If worse come to worst, I'm sure you could claim a new vehicle purchase on your taxes if you end up having to go bigger.
Lisa T had a good idea to test it out ahead of time so you know you'll be able to leave the hospital in one car. Man, I never thought about carseats for mulitples...crazy stuff. Congrats on the triplets!