I don't think that the TSA is open for access into the terminal at that time. After the last TLV flight (10:50p) the next departure is at 11:55p on Saturdays (BON) or that 5:30am flight to IAH the rest of the week.
If they are inside there aren't many comfortable places to hang out. The chairs all have the arms built in to them so laying across them is not so great. But if they like sleeping on the floor they'll be in for a great night.
Sleeping In Airports has a pretty decent collection of reviews.