More police statements (from the top of my head after reading many articles today from local news:
At first police thought they died of gunshot wounds to the head, but they aren't 100% sure and are waiting for autopsy reports.
The parents both say that they thought both were at home in their own beds, so it wasn't a "they stayed out too late" situation, but a "snuck out" situation.
To answer a question, I think I saw somewhere that they were *not* dating, but I can't remember if it was an official statement or just a commenter on a news article, so take that with a grain of salt.
This is part of an area now known as The Heroin Triangle, primarily because of upper-middle and upper class adults becoming hooked on Rx meds, then switching to heroin when their doctors cut them off. Meth isn't as big here as in some other parts of suburban and rural GA.