I have to vent...

The past two weeks have been really rough caring for my dad. I believe he is slipping cognitively and I am going to have to figure out what to do about it.
I had a nice week and a half of my life back while my brother and sister helped to take him to his radiation appointments. He and my brother had a huge blow-up yesterday, so now my brother is out of the picture and that is probably for his best anyway.
Dad vents a lot to my mom. A lot of things I would never hear of otherwise. He is so different with me; easier on me, I guess. I have seen some childish and irrational behavior from him, but usually it is directed at his doctors or treatments. He told my mom he would have shot my brother if he could have, so now I have to slip over there Tuesday while my sister has him at his appointment and remove all guns from the house (my brother already took all the bullets out 2 months ago when he was hospitalized to remove the tumor as my dad had hinted at killing himself).
I figure this is how those kind of tragedies happen...someone didn't take such talk seriously or step in to prevent it, and that's not going to be me. It will make him mad at me (he was already briefly mad at me for not letting him drive interstate when his car was in the shop Monday). There would be nothing to stop him from driving to Walmart and buying more ammo. Eventually I am going to have to take the keys altogether, although I think he is currently safe to drive around town.
I am trying not to have to take everything away from him all at once. I'd like to think that he wouldn't
actually shoot someone, but when he gets angry at people he says these things and this is the 3rd time this month (two other people/occasions). I think he is just lashing out and venting, but I have to be proactive here.
Between the large tumor that was removed, swelling on the brain, damage done by the surgery itself, one of the side-effects of Keppra (anti-seizure med) being irritability, side-effects of radiation to the brain and possibly dementia from the Parkinson's he's been living with for 25 years...I know it is not him talking. He is not himself.
This is hell. A nightmare. But I have to be brave, calm and rational and just simply do what needs to be done. It is such a shame, because he is doing so well with the radiation and chemo itself. It should buy him at least another year of life, possibly more. I don't know if the cognitive damage is permanent or what. It's hard to see any good outcome with this going the way it is.
He is physically well enough to live on his own right now. I am hoping that once he is done (3 more weeks) with the treatments, that he will simmer down once he is not being pestered on a daily basis.
I am trying hard to hold on to some kind of normal here in my own home, for my own family. That is hard. I can't let this consume me. I was really upset last night after hearing what had happened with my brother, but I have peace about it today. It comes down to staying clear-headed and not getting emotional. I have to make the hard decisions, the wise ones, no matter what.