I agree with jmhyer.
To the OP...I used to have a house exactly as you describe. Make a plan and communicate the plan to the entire family.
Some other things to consider in you HD plan:
Most times you would not have time to gather the clan so educate them. Tell them a command you will give which means to lock down in their room until the all clear is given. Make it short a sweet.
Have a weapon (you already do), a cell phone (in case the home phone wires are cut) and a good working flashlight (in case the power is cut) and a key to your house on a key ring with a brightly colored fob or "boat float" (for throwing out the window to the police) in your safe room (master BR in your case).
Find a position where you can get low and cover the point of access to the upstairs. If possible have someone else (wife etc) call 911 so you can stay focused. Instruct the police to come to a specific window to receive the key. This way they don't have to break down your door. Tell the 911 operator to give the police a password to use before they come upstairs. Have them call your name and give the password before you lay down the shotgun and step away from it in plain view with your hands empty and up.
HD plans can save lives.
IDPA Member A00640
Founding Charter Member - Middle Tennessee Shooter's Club