I've gotten my mother a succession of ereaders going back to the Rocketbook.
Currently she's using a Paperwhite and a Fire 8, both tied to my account. She uses the paperwhite for purchased books and the tablet (that I got her to read online news and do word search puzzles) for the Prime Reading library.
One point she loves about both gadgets that gets glossed over is weight.
eReaders and tablets are lighter than most print books, especially hardcovers.
At her age the large print and weight aspects, well, they "weigh heavily" in favor of digital.
As for sharing, it happens automatically. If I buy it, she has access to it.