Critics offer two interpretative views on The Turn of the Screw. One is that the story is only a ghost story such as were popular in the 19th century. The other is that it is a psychoanalytic study of a woman's insanity. If the first is the case, then the central question to be resolved (meaning conflict to be resolved) is how to protect the children from devilish ghosts who mean them harm. This is complicated by the injunction laid upon the governess to refrain from notifying their guardian about any of their concerns.
If the latter is the case, then the central question to be resolved (again, meaning conflict to be resolved) is how to recognize the governess's insanity so as to protect the children from her--if indeed there are children and she ever was a governess. This conflict would be between the children and the governess--assuming for the moment they exist--rather than between the governess and housekeeper, Mrs. Grose, who appears to support the governess. If neither the children nor the governess as such existed, the the question (conflict) is how to sort insanity from reality. This is complicated because there is logical order ans seeming rational behavior within the context of what would be insane hallucinations.