If it were my own home, I'd be armed, so there would be no problem. Not sure that would apply if this is some random house in the middle of nowhere though.
I like to think I would grab the closest thing that could be used as a makeshift weapon and try to surprise him, like maybe club him over the head with something. It may not be the smartest thing to do, but there's no way I could live with myself if I hid there listening to my friends get murdered without trying to do something about it. I'm not pretending I'm Bruce Lee or Jackie Chan or someone (because I am definitely not), but I'd try and hope I got lucky. If I managed to surprise him out of nowhere, it might work.