Should a sibling share parent’s major health problems like when EMT is called or hospitalization is needed?

Dad has Dementia, not competent. I so hope you have immediate POA if not and you need a Dr. to declare Dad incompetent to make informed decisions, get it done. Then give all his doctors and the hospital he frequents a copy of the POA. I know at Moms regular hospital, POA shows up on the Admitting screen. At heir house, does that mean Mom is still alive?

5 years is a long time. Maybe Dad should not be alone anymore.

Yeah. No. I don't know why you talk to them either.
Seems a waste of time to me.

If your dad has been an ass to you your whole life, why in the world do you continue to do anything for him? I mean really. Or are you just a sucker for punishment?
NO child that was abused in any way by a parent should ever take on their care when the parent gets older and needs help.
Your mom and dad need to now figure out their own care needs, by either hiring in-home help, calling an Uber when needing a ride to an appointment, or better yet moving into an assisted living facility where they will have paid folks checking on them throughout the day and will have rides available to any and all of their doctors appointments, grocery stores and the like.
Your family is dysfunctional(as are 99.9% of most families, so don't feel too bad), so not sure why you would expect anything different from your "bad kid" sibling.
Instead just step back from the dysfunction and start living and enjoying your life.
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I have medical and financial POA and have legal access for all medical things. My dad does these silent treatments until he needs help and I end up stepping in because there is no one else. He began dementia stages 5 years ago. My sibling left before the pre surgery appointments and hasn’t been back since saying their pet needed surgery. And they got all angry and over reacted to my inquiry about how come they didn’t say anything to me when they found out about the surgery.

When a parent cannot 100% care for themselves or are not all there, I think that siblings should share what’s happening with their parents health stuff no matter what the sibling relationship is like.

My help consists of grocery shopping, fix things at their house, pick up Rx’s, drive to appointments, and many other errands.

You do not indicate that your parent(s) have any medical conditions, you do not indicate if there is dementia involved.
Do they have a POA? If so who is POA?
What kind of help do you provide?
Frankly if your parent is cognizant and they told your sibling not to say anything to you your sibling was abiding by your parents wishes. Even if you were informed if your parent told hospital staff not to allow you to visit they would have not allowed you to visit. If you are not listed on the HIPAA forms the doctor or hospital legally could not have informed you as to your parent condition.

You are under no obligation to care for them if they do not want your help.
If they have abused you in any way then you are wise to back off and not have contact.