I don't doubt your good faith, or your abilities, for that matter, but this has the potential for true catastrophe all over it.
Lessee, we've got an intruder in the house, we've got unarmed parents wandering around the ground level investigating the bump in the night, we've got one armed son on the second level intent on clearing the house, and we've got a second hot-headed son with an SKS looking for something that needs killin'.
Q1: No.
Q2: No.
You also need to sit down with your entire family and seriously hash this out before the need arises. Who goes where, who investigates (you might give consideration to letting the po-po do this, unless your house is really out in the sticks), and who stays the hell in his room (guess who that is?
)
Presence of other/younger siblings obviously colors your plan, as does the physical plant - the actual layout of the house, number and location of available exits, surroundings, etc.
God bless you for taking your responsibilities seriously, but do be careful! As mentioned, you need clearly delineated responsibilities and a plan in hand (and mind) before the fact.