Who's the landlord? Presumably he'd care that some other people are secretly living in his property rent free w/ no sort of background check or anything.
Granted, if you were going to "rat them out" you probably shouldn't have so outwardly expressed disdain towards them, cause now even if the landlord finds out independent of you calling him, your two roommates will assume it was your doing and well...you have to live with them after this.
It also depends on how long theyll be there. I dont think two weeks is that long. And one of them can say some friends were staying over for a little and probably get away with it.
Yes, if it actually is only 2 weeks...
Even then, it depends. I know my apartment would never allow guests to stay two weeks straight if they knew about it.