It's a tough situation, I sympathise. I have a small family - just me and my brother now - and when my nan, DF and uncle died, my brother was nowhere to be seen. He did come to their funerals, but didnt pitch I
to help with a single thing. He claimed he "couldnt cope" with hospitals, so didnt see my dad on his death bed.
Then my lovely mum was all alone, and of course I stepped in to help for 11 years, because I adored her. She died aged 84 in October this year. My brother, this time, again didnt come to see her in hospital, but also didn't come to the funeral, didnt help with any arrangements for anything. He is co-executor but he doesn't have time for that - happy to take the money when I've sorted it all out and has generously told me to "take what time I need" to get it done.
It bites, honestly. I didnt mind doing stuff for my mum as I loved her. But it rankled that my brother never did a single thing, and my mum wasnt dumb, she noticed. I would remind him of Mother's Day, anniversaries etc. I remember once he came to visit mum, years ago, and stayed for a week. He made my mum run around doing everything for him, poor old lady was run ragged. I said, while he was there, please could he help her sort out something on her Sky account I hadnt had time for. Guess what, in a whole week of doing nothing he simply "didn't get time for it."
I think you need to at least TRY to mention it strongly to your family. The thing is, they have decided you are default in charge of the decisions, of the caring. It entirely rests with you. None of them, on their own initiative, will DO anything. They just leave it to good old, willing you. But at least if you do specifically allocate tasks you can see what response you get.
You could try a guilt trip. "Dad mentioned, he's worried I'm the only one carrying all of his care. It is true, I'm run ragged. You did offer to help when mum was dying, and now I need help as I am completely overwhelmed. So I need you to do xyz."
You could also be more direct. "Look, it rankles that you simply assume I'm going to do everything. I do it because i love dad and he knows it. So when you do nothing, what do you think he takes from that? You arent useless, and yet you choose to stand by passively. You never check in with me, you never offer to help. It goes beyond just a lack of care, it speaks to a truth that you appear not to love him, and by extension mum too, since you promised her you WOULD help. For dad's sake, it would be nice to evidence your love by actually being there to help him when he needs you. Dad knows you'll gladly pick up your share of the inheritance when the time comes, and honestly I don't know how you can live with yourself. Are you really so selfish that you can't see what you're doing to dad, and to me? I've kept my peace for so long, but I had to say something because dad has what, a maximum of ten or 15 years left, and for the last 5 you've done naff all. You've still got time to salvage your relationship with him and with me, if you want to keep the good opinion of either of us, if it means anything at all, then STEP UP."