My kids have always been side by side from birth and there isn't much fighting. When I had just one kiddo she was in the middle. When baby #2 came she was in the middle with baby #1 beside her. When baby #3 came my oldest two stayed side by side and baby #3 was beside them. Fast forward and they're 3, 6, and 7 and I couldn't separate them now if I wanted to. Happy as clams, so don't let the 'kids fight if they're beside eachother' stuff worry you. Your three kids are side by side now, in utero. I wouldn't be surprised if they are just fine in the vehicle because, if you do a three across from birth, they won't know any different.
I've done triplets in a Grand Cherokee, and recently helped a family expecting trips who already have two small children. They bought an Ody, which I get.
You could do three across quite easily in a Pilot, Armada, Seqouia -- basically you want to look for a vehicle that offers a 'real' middle seat in the 2nd row. None if this 60/40 stuff where you're dealing with a 30/30/40 scenario in reality. You want that middle seat to be as 'real' as the two outboard seats. Avoid narrowness, plastic hinges, humps, and anything else that looks like it might make seat installation funky.
Look for infant seats that are straight - not flared along the base. The Graco Snugride 30 is both narrow and straight, and fits preemies well. That's what worked in the Grand Cherokee (and later Roundabout 55's when the babies switched to convertibles).
Anyway, totally doable. Just need the right vehicle and right seats.
Eta- I just remembered I've actually done trips in a Seqouia (can't spell that word). There was of course tons of room. I think, though, when you're loading someone to the middle you really need to decide if you want such a big rig that running boards and a huge step up is what you want. Also, it's a reach to the middle in these high, truck based SUVs. I know I've posted it 4000 times now, but the Pilot just seems to .. work. I have yet to encounter a scenario where it doesn't work, and it's low. I'm 5'3" and can stand on the ground and reach to the middle to load and buckle a kid.