Per wiki policy, Spoilers Off applies here and all spoilers are unmarked. You Have Been Warned.
Tracy finding out about living in the murdered family's house was a ploy by Bughuul to drive the family out, and thus kill them quicker
After all, she found out via Ashley, who had already had contact with Stephanie. Tracy's explosive reaction seemed to strongly suggest that she was going to take the kids and leave (not necessarily Ellison, just the house). One imagines that that would be a wake-up call to Ellison, who would then leave with them.Trevor's night terrors consist of future visions of Ashley killing him and his parents.
Unfortunately, the nature of night terrors is that the person can't remember them when he wakes up, so the "warning" accomplishes nothing.