The Death Mansion of No Escape

Princess Twilight Sparkle, Rainbow Dash, Pinkie Pie, Rarity, Applejack, and Fluttershy are visiting an old mansion, its origins, and age both unknown. Over time, some creatures have made it into the mansion and began to trap all other creatures that enter, with no chance of ever leaving unless the three in charge allow them to leave. But only one pony's been allowed to, and everypony else had died without a trace. Or so it seems.
No matter day or night it is, once you step inside, there's no leaving. And if you can't escape, you die to the hands of the monsters there, killing your friends and turning them against you, leaving them in a grotesque mess until every last pony is dead.
As the six friends explore the mansion, nearly clueless, Rainbow finds a diary of a pony who had stayed for three nights before she died, along with two of her friends. As she reads the first few sentences of her first entree, they all realize this place isn't just any ordinary old mansion. They try to escape, but as the diary said, once you enter, there's no escape.

Three nights. Four left to die. Two of Equestria's first possible survivors in years. Who are they?