In the last 10 days of my father's life, I took some of my annual leave and went to stay with my mum so I could take her to see him etc. Because it was an emergency situation, I didn't have time to do proper handovers of my clients and had to sort out lots of work stuff over the phone while I was away.
It was a bloody horrible experience. My father looked like someone just released from Belsen, he didn't recognise me because of his dementia, and my mum was in the early stages of dementia and kept talking about when DF came home when it was very clear that he never would. Every day I'd take the dogs out and cry from sheer frustration and desperation.
I would have done anything to avoid it. I also wished like mad that my brother, who doesn't work due to poor mental health, had been well enough to share the burden. He managed to come up for one day, and visit once, when really he could have stayed the whole time. I know from long experience that it's pointless trying to get DB to do anything he doesn't want to do, so I didn't lash out at him, but if I had, I'd've called him a lot worse than fuckwit.
After 10 days, I came back home and DF died the following night, so I had to go straight back up (they lived 150 miles away) the next day, taking this distraught and demented woman, who used to be incredibly strong and capable, to registrar, undertaker etc and sort out the fucking funeral.
So I can get where your DB is coming from, and how the burden is pushing him to the end of his tether. Forgive him and don't take it personally. Ask him what you can do to help and do it.
I'm also a bit mystified as to how you changed jobs because the hours you were working were too long, and then found yourself doing 72 hours at a stretch. Did you not check working hours/shift patterns before you took the job? And I'm assuming that you've signed away your rights under the working hours directive, in which case you've only yourself to blame.
Grow up, grow a pair, and take your share of the burden.