Subjectively, I am thinking the placement of the bar stools was for another reason.
Evidently, the investigation has not uncovered any evidence that the victims feared either a specific, nor a general threat. Thus, I dont think they were placed there out of fear.
Rather.... my guess is that they were placed there out of a desire for peace and quiet during "after hours". The house appears to have been pretty open and had multiple resident who seemed to be socially active.
When applied to college housing, this could mean a steady stream of friends, friends of friends, and "Know you from party "P"- hey, got a light?" and "Car wont start, resident "R" said I could crash on the coach" type aquantiances coming by at all hours to talk, drink, study, borrow things, resolve an "emergency" etc.
Thus, bar stools blocking the sliding glass doors could have been their way of saying: "No more of anything after 0200- well, at least not usually."