First, get a plan. You have the home court advantage, and you should use it. My family and I live in a small apartment. Nonetheless, I know where the weapons, the backstops and the blind spots are.
Second, teach the whole family the plan. My daughter has already been taught where to go and what to do in the event of a tornado or a home invasion. My wife has the same information. I don't know how old your kids are, but they don't really have to be very old to understand something like "if bad guys get in the house, get behind your dresser. If they get to your room, stay there & fight & scream."
Uncle Buck said it well:
Originally Posted by Uncle Buck
I can replace the TV, the computer, the "Stuff".
I am going to pray like there is no tomorrow that nothing happens. I will be prepared if it does, but I am not going to be active in trying to push anything to the next level.
You have an advantage. You know your kids are upstairs with you. Play blocking force at the top of the stairs and do not allow anyone to come up those stairs. You most valuable resources are already up there with you.
If your wife and kids are upstairs with you, then you have everything that you really need. All of that "Stuff" can be replaced. Your kids cannot.
I would also add that I can't tell from the OP if your kids' rooms are upstairs or not. If they are, great. If not, and if there's an extra room up there (guest room, home office, etc), consider swapping some rooms around. Having everyone upstairs puts you in a pretty good position to use the stairs as a chokepoint.