I read some posts, not all, whatever you do don't "protect" the kids from seeing their dad, life is tough and cruel in parts. Not letting them see their dad or say goodbye will do massively more harm than keeping them away long term.
Go to the hospital, take the kids, kick some nurses in the uterus if required. Most likely they will all, or some will be willing to help, will have a family room or someone who can sit with them for a bit so you can see your dad yourself for a bit.
it likely won't be great, for your or your younger siblings, but protecting people from pain like this usually just causes repressed pain that lasts much longer, with many more consequences. You clearly want to be with him, if the kids know it or not they want to be with him, if you mum knows it or not, keeping you all away is the worst thing for you, her, and your dad.
You often hear parents with things to say like "I don't want them to remember him like that", it almost sounds like a good idea, till you realise kids can imagine how bad he looks anyway, having no memory will only send the imagination into overdrive, and not being able to say good bye will do WAY more harm than seeing him sick in a hospital.
Parents always want to protect kids from harm, and generally come up with the worst way to do it, kids need less protection, they'll be much more visibly and outwardly upset than "hiding" them away, but otherwise they'd end up feeling that pain, inside, not expressing it and having it eat away at them for years, maybe forever.
Pain, better out than in basically.