if you had a gun you could
A gun isn't going to help you stab people. If the person being victimized had one there is a good chance it could protect them, but it would not really help the perp in most imaginable circumstances, not in most crimes of violence are people stabbed while held at gunpoint. There is simply no evidence a gun was part of this crime at all.
As far as stabbing four people dead; under several of the possible conditions, it may not just be possible but not difficult at all. Let's just say two of the people were relatively small and not physically strong, and to one degree or another intoxicated. Let's say the other two victims, the male and female, are themselves deep asleep. and the other two unidentified and unharmed people living or visiting there were also deep asleep.
A single deep thrust into thorax or throat is going to prevent anyone from screaming, or even making much of a sound at all.
Also you and I may not imagine ourselves as perps, so we are not thinking from that perspective. But most people would be surprised how much the initiative and surprise in a violent act give the attacker a profound advantage. You and I might picture a violent act as th result of some kind of escalatory series of events. But in fact if you just haul off and stab someone deeply in the thorax, they are not going to make a peep, and the second victim is likely as not to simply freeze in shock. The young man and woman victims may have been deep asleep. If wakened a bit they may not have known what they were hearing if they heard anything. I lived in a place with with four of us roommates and various guests and goings on when I was a junior in undergrad. There were unfamiliar noises all the time -- I just put the pillow over my head and went back to sleep.
We also don't know if there were multiple perps --although I think it could have easily been one.
I just think there is an observational bias among all of us who are sane and not murderers. Anyone with basic close combat training, or anyone who grew up in a bad neighborhood or home knows that surprise initiation of violence is a huge advantage. You do not telegraph what you are going to do in word or deed. You just do it. It is why it is wiser to sucker punch someone, or hit them on the back of the head with a brick then to announce you are going to be violent.
so we don't know how this played out. But I can think of a half dozen scenarios where a military age male with a kitchen or camping knife killed three petite persons and another military age male without other people in the home knowing or even waking.