I am only a few chapters into THe Haunting of Maddy Clare so I do not have a good impression of who the characters are yet, but I will give it my best shot. There are so far 5 main character introduced. Sarah Piper, Mathew Ryder, Alistair Gellis, Maddy Clare, Mrs. Clare, and Mrs. Macready.
Maddy Clare has not yet been seen, she reminds me of Greta Gerwig a bit waif like.
Sarah Piper is a typical woman of the 1930’s I think Ellen Page would be good in this role. Starting off fragile, but I see this character having moxie.
Alistair Gellis is a vet of WWI, with scars both visible and invisible he would be played by Jake Gyllenhaal. Kind of upper-class, with a bit of edge to him.
Mathew Ryder my first thought was Hugh Jackman, but the age is wrong. Maybe, Ian Somerhalder.
Mrs Clare would be Helen Mirren.
Mrs. Macready would be played by Susannah York.
As for who else is in the book I do not know yet. Nor, do I know who would make a good director. I am just not that far into the book.