First, I'd just recomend you get the family together and talk it over.
If everyone looks over the facts, it may be easier to work something out
Right now, I'd see if your brother would leave his SKS or 20 gauge with your dad.
What I'd recomend: Dad has a gun, you have one as well. Work it out a "Plan" on what do do. Ask your brother (Phrase it this way as well), to remain upstairs and call 911, this way there is a always-open 911 line, and as "backup" (All of this will sound important). If there are shots fired, pre-arrange some kind of signal, and then decide on what to do.
Right now, our plan is no one leaves the rooms. Me and dad's rooms are within 15 feet of each other. We stay within the doorways, so anything in between AIN'T US. Only after we sorta figure out who's who, we look around more. Everything's one floor, and really open (Only 2 closed off/unseeable rooms), so it is alot easier for us.
Regardless, I sortof plan on getting a home-alarm system. Only problem is we have a driveway alarm, and all the freakin animals keep setting it off
I don't know what we'll do with something circling the entire house!!!
To the comment above: I was under the impression that the father was willing to learn,etc. just that money is tight enough that he didn't want to yet?