The aliens don't enter the house and keep their distance for most of the night, because they don't know what kind of weapons the family has. The first alien to go inside the house was easily subdued by Kurt, so they keep their distance until they've kidnapped enough of the family members.
The implication that the McPhersons have been abducted before, (as evidenced by apparant neck-implants they've been given.) The TV cut, unfortunately, uses a Talking Head to blatantly tell us this instead of letting it be implied.
The implication that this could have all been avoided had Tommy simply not brought the camera with him, since after they shoot one of the brothers in the hand at their first meeting (which the brothers infer happened because the aliens thought the camera was a weapon), the aliens take no further hostile action until after Kurt shoots and possibly kills one of them. In fact, the alien that discovers the camera seems to be careful not to hurt Tommy during his search, as Tommy goes into a trance when the alien enters the room and has no memory of the event afterwards.
