If they were downstairs, I'd call the police from our bedroom, then step out of the bedroom and pull the panic button that is fitted to the alarm system. I imagine they'd scarper at this point, but on the off chance that they came upstairs and tried anything I'd defend myself as I felt necessary with anything that came to hand.
I wouldn't go downstairs to take anyone on. Why would I? I don't have a gun or even anything particularly heavy or sharp, and I'm not a fighter, so I'd be running the risk of being killed or seriously injured. I've no intention of looking for trouble I've got everything insured, so they can take what they like and I'll claim it on insurance.
If they came upstairs, then all bets would be off and I'd defend myself and my family as best as I was able with anything that came to hand.