I think a problem with many of these books for modern readers - especially Americans - has to do with different writing styles, too. Contemporary people can have trouble with the long sentences and sentence structures of 19th century literature.
It takes more concentration to read Dickens or Bronte, compared with a Hemingway or even with most vaunted contemporary ‘literary fiction’ - and certainly with whatever they’ve been reading in high schools in recent years.
I got my oldest hooked on Bernard Cornwall which lead to CS Forester and then to Robert Louis Stevenson.
It gave him the start on vocabulary and a bit of history.
Start with the current age and start taking them back through history.
By the time you get to Shakespeare they have the vocabulary to understand what they are reading.