I recently read
Notorious Royal Marriages by Leslie Carroll, and though I know that books like that are not the most accurate it is a good book to get quick overviews of different royalty and the chapter about Sisi was very interesting.
In it Carroll seemed to think that Sisi was not particularly close to any of the children, except for Marie Valarie whom she seemed to never want to leave her side, Carroll questions her paternity as being other than Franz Joseph but I've heard otherwise before.
Also, Carroll blames Sisi's psychological problems and her mother-in-law's distrust/dislike of her for the reason she was not close to her older children. An interesting bit about Carroll's reasoning for Sisi treating Gisela poorly is that she blamed her for little Sophie's death, something about Gisela being sick first, though she also states that Sisi took the children on the trip against her mother-in-law's wishes, so it might have been self blame. Otherwise she only speaks of Rudolph's psychological problems and how they mirrored some of Sisi's, though Carroll also blames a tutor of Rudolph's for firing guns in the air to get him to focus on studying, thus leading him to an obsession with death and guns.
I would love to read actual books by scholars devoted to this family, so if anyone has any good recommendations, especially concerning the children, I would love to hear them!
I know this isn't the best source for the information but I thought I'd share one author's account on the family dynamics. Also the books is pretty good and very quick read and has wet my appetite for reading more things about royal families I know so little about.
(I apologize for any name spelling errors, also any information I botched up as I do not have the book in front of me, loaned it to a friend, and the internet provides crazy variations of spellings)