Keeping them from upstairs (family) is paramount to me. So I'd position myself somewhere I can view the stairs and stop anyone from going up. Then I'd wait - if they go away, fine. But I sounds like thier doing a thorough search and will come my way or go upstairs.
So I'd prepare myself to shoot at either moment and pray thier are together at the time - don't want a survivor blasting away at blind noise and suspected threats which will mostly likely becoming from upstairs as well as my guns muzzle...
Not good - but more than likely they will be off at the first shot. Guess I'd risk that to save having to shoot both of them down without looking down thier muzzle's first.
Heck - I'd probably rethink this as I waited and shoot both as soon as they come into view at the same time. I'm leaning toward it already as I typed my first response...
Yep - two down leave no danger to me or family. But I'm still waiting for them to come into my area where I monitor the stairs or the stairs themselves...
There's also always the problem of them having more friends out of sight who'll will act to help thier dastardley buds when the music stops.