You don't see the monsters leave the houses after they've killed, you dont see how julie got back to the house after she got teleported through the tree and you dont know nothing that happens between Boyd/Sara seeing the light outside the tent and them waking up the next morning.
Based on 'the box' scene, the monsters seem to be physically capable of breaking through windows/doors, but never do for some reason. They could easily get in houses strength wise, but instead, need someone to let them in. It raises questions like, would the double door incident that saved fatima and ellis have worked if it wasnt for the townsman/talisman or whatever those stones are called? What was it like to live in the town before the discovery of those stones? Did they have to go in them underground shelters every night? Maybe I might have missed some details.