Here is what I have in mind. Please tell me where it is wrong.
One place that holds everything about your relative's care: Their medications, appointments, who is doing what, the hospital letters, the council paperwork. You do not type it in. You forward the email, or take a photo of the letter or the pill box, and it fills itself in and shows you where it got that from.
Then it hands that information to whoever needs it, in the form they already use: A printed sheet for the fridge with a code a paramedic can scan to see medications, allergies and who to call. The same summary on the phone's lock screen. A link you can text to the GP or the care agency. A one-page summary for the hospital, or the evidence for a carer's assessment, ready for you to check before it goes anywhere. And when someone scans the code, you are told.
The rest of the family sees as much or as little as you decide, and the ones who never open anything get a short summary once a week.