It's better to get separate rooms. One might think "We're not going to do anything." But there are other things to consider:
1. The example it sets to the rest of the hotel guests.
2. I know what girls' hotel rooms look like on road trips. There are generally clothes and shoes all over creation, as if some hurricane annihilated the room. Guys don't need to see the personal stuff, just as the girls don't need to see the guys in their PJs and boxers. In other words, it's pretty difficult to maintain modesty in such close quarters.
3. All of the parents would probably feel a lot more comfortable with the teens in different rooms, so it would honor them as well.
4. Just because you think nothing will happen, this does not mean that all of the other teens have the same intentions.
Whenever you have questions on purity or modesty, know that it's always safe to err on the side of innocence.