There is a description of the manuscript Reminiscences of Aunt Jane as written to the author's brother, James Edward Austen-Leigh who is the author of Memoir of Jane Austen. There is also an introduction to the Reminiscences.
Additionally, there are summaries of the other continuations:
Somehow Lengthened: A Development of Sanditon by Alice Cobbett, Ernest Benn Limited, London (1932) 316 pages.
Sanditon by Jane Austen and Another Lady [Marie Dobbs] Houghton Mifflin, Boston 1975 329 pages.
There are very detailed, line by line, notes for this continuation and Reminiscences.
The continuation of Jane Austen's fragment is itself a fragment. And, in fact, seems to be only a draft. It takes up exactly where JA left off. Charlotte Heywood and Mrs Parker awaiting the arrival of Lady Denham in the sitting room of her residence, Sanditon House.
The story is moved forward very little. But, we meet Sidney Parker and a new character, his friend, Mr Tracy. The development of SP is quite promising; he is handsome, rich, intelligent, witty and good-hearted. The character of Clara Brereton is also developed as a poor relation of Lady D who believes in pursuing her own best interests without regard to how it affects others. Of the characters that JA had introduced, they appear in this story quite unchanged; Mr and Mrs Parker, Diana Parker, Arthur Parker, Lady Denham, Miss Lambe.
The continuation ends just as abruptly as does Austen's fragment.
I think that this book may be of interest to JA scholars but not to
someone who wants to read a story.