Seriously, brother, Consider moving Dad the F OUT of CA. Yeah, I know he is attached there, Probably has a home paid for that he hasn't disposed of, or some other stuff, but your family isn't making this any easier on YOU.
California, No matter how beautiful it is east of the Sierra (for example), it is not worth the headache to move there for any reason whatsoever.
Simply moving somewhere to wait for someone to die, really isn't going to work out. If you are the guy who has the ability ("they aren't doing anything, they are retired") to take car of Dad, then the others should take care of cleaning out the house, and disposing of his collection of items, and the real estate.
If he is with it enough to make a decision, there needs to be a Trust formed, so that all questions of who gets what is taken care of in advance. LOTS of headaches created by end of life situations. I've seen screaming matches at the bedside, when the guy hasn't even achieved room temperature, because of this sort of thing.
The people taking care of the person in question also don't get near enough credit for their sacrifices from the rest of the family, only tons of criticism and accusations, and never lift a hand to help.
Leaving your firearms somewhere else and changing your residency presents some iffy questions. Make sure you have power of attorney for both life matters and medical. Amazing how little you can do without that taken care of.
This is only a light sketch, but I have seen far too many people make the wrong decision when an alternative could have made life easer for all concerned. Say out of California, no matter what.