There are really three issues being discussed here:
1. What type of load to use in HD
2. How to deal with penetration issues
3. How to respond if the premises are actually breached by a BG
The problem is that any effective load used under the described situation is going to have penetration issues. So.......
Get some buckshot, I use #4, but anything from 4 on up will do nicely, then, develop a plan so that you can defend the 2nd floor with all famly members being safe. This may involve changing bedrooms or some other type of reloacting family members or maybe not. The important thing is to HAVE A PLAN. If you do not, then you are setting yourself up for either failure to achieve your objective or a disaster.
My plan is to defend the 2nd floor, when I had kids at home they were located in the safest room from my (or my wifes) gunfire. After that I plan the bad news for the potential intruder. The first issue means that family are behind me or absolutely out of any possible line of my fire-I cannot depend on the intruder to be as safety aware as I am, so the objective is to stop him before he can put out rounds.
Everyone is concerned with their fire and penetration, but how about the BG? And he cares a lot less than anyone else about where his rounds end up.
BTW; my plans never include room/house clearing. Even though both my wife and my self have 66 years of military/LE experience between us, even two trained people should not do clearing ops. Even if you do know your house better than anyone else. The idea here is Home Defense, the operative word is defense. When you start clearing rooms you are now on the offensive. Without regard to possible legal ramifications, your mission is to defend yourself and your family. The on duty police can catch the BG(if they get there in time). It is also a really bad idea to be moving around with a big gun if the police are expected, not all of us are really smart, or calm in the face of excitement.
My SOP calls for me or wife to call 911, tell them exactly where we are going to be located, and then wait. Wait till you know the police are there, and then make verbal contact before you show yourself, call 911 back to ask if they are on the scene if necessary. When you show yourself to the police, do so without a weapon-this can be so important as to be fatal.
I know this type of planning seems paranoid to some, but it can be a lifesaver, and I don't care if the BG gets away, my objective is safeguarding me and my own. Another thing to remember, if you are taken out of the equation, your loved ones may then be helpless, that is why I defend me first.
And why I do not go offensive.