I, too, am hoping that LE being so quiet means that they're busy gathering, verifying, and organizing the necessary information they need to arrest a suspect. If they're not asking the public for more help, I'm hopeful that it means they don't NEED the public's help, because they have a lot of good information already.
Statistically, it is more likely that ST and MT were murdered by someone they know than by a stranger. There's been a lot of discussion in this thread about the house's doors, locks, points of entry, and how someone could have gotten in, but my hunch is that a break-in wasn't necessary because it was a friend or family member already in the house. Someone who was either invited for a visit (it was the holidays!), or maybe a relative who had been temporarily living there.
If the Tepe family had a relative (or relatives) visiting or staying with them, that could explain the "...or anyone who lives there" comment the caller made. It could explain why there was no sketchy stranger/masked burgler for neighbors to notice. It could explain how the murderer was able to commit the crime so "easily," without signs of a break-in, struggle, or robbery. It could explain why friends and co-workers so quickly suspected the Tepes needed help - maybe they knew, from conversation with Monique or Spencer, that they'd been having struggles with a family member (maybe related to substance abuse, mental illness with violent tendencies, threats, etc).
I find it interesting that the Police are guarding at least two different households with relatives of ST and MT. It makes sense for them to guard the house where ST and MT's children are staying, since they could potentially be in danger from this un-arrested murderer. If the murderer doesn't know which house the children are in, guarding TWO houses would be a good way to throw him off, maybe...? Or maybe there's a larger family dispute of some sort going on, such as the murderer being a relative or family friend that some family members suspect, while others are trying to protect. Maybe one family member turned in another (or a family friend), and is now in danger of retaliation from other family members, or something convoluted like that. Maybe LE are guarding the houses of family members who have received threats.
I'm doing a ton of speculating, I know. I have no real info. I just think that these murders are likely to be deeply personal and targeted, a result of the rage of a relative or "friend" of the Tepe's. I'd guess that the door locks and security system aren't so relevant, and ST and MT were more likely betrayed and blindsided by someone they had in their home. My heart breaks for them and their children and loved ones.