1) I agree, solo house clearing is rarely a good idea.
2) Capacity wouldn't have helped if multiple people, all with clear lines of fire, decided to engage. Capacity could have helped if a good defensive position had been established, which would have limited lines of fire. "Chokepoint" and "funnel of death" come to mind.
3) As a 15 year old high school wrestler, I probably would have gone and checked on the noise, too. As a 43 year old, trained shooter, I would try to establish a chokepoint instead, keeping myself between possible bad guys and my loved ones. (Of course, at home I have two med-large dogs, and a small and loud dog; odds are they'd alert, and that would change things quite a bit.)
4) There is no shame in bunkering and calling 911, though there are times (family members in other parts of the house) where bunkering may not be acceptable to us.