A. Forenames: Oscar, Peter, Shirley, Ruth, Ruth. Surnames: Zaniewski, Yorke, Underwood, Valdez, one of them (not Valdez) twice. Books: Faulkner's "Light in August" and "Absalom! Absalom!", Porter's "Ship of Fools", Woolf's "To the Lighthouse", Hemingway's "The Sun also Rises".
B. At least one of the siblings is a woman (by #2). The women are two Ruths and a Shirley, and Shirley isn't a sibling (by #1). So, assuming (I think fairly) that we don't have two siblings with the same forename as well as the same surname, the siblings are Ruth X and either Oscar X or Peter X. The latter must be the one in #3 who chose Hemingway's TSAR; then by #2 the other man chose something by Faulkner.
C. X (in B above) is not Yorke (by #4) nor Valdez (by #5) so it's either Underwood or Zaniewski.
D. Yorke chose a book without "light" (by #4). It wasn't TSAR because that was chosen by Oscar/Peter X (by B) and X is not Yorke (by C). So Yorke chose either Faulkner's "Absalom! Absalom!" or Porter's "Ship of Fools".
E. If Yorke chose "Absalom! Absalom!" then the fifth student mentioned in #5 shares Yorke's first name or author. (Not surname; by #4 there is only one Yorke.) If it's the first name then that name must be Ruth (by A) so that fifth student is Ruth X who has a sibling. In this case we have Ruth Yorke who chose AA; Ruth X; and Oscar/Peter X who chose TSAR. Then the other man chose a Faulkner novel, which (since Ruth Yorke isn't the other man) must have been LIA. Now return to #5; Ms. Underwood isn't Ruth Yorke, nor Ruth X (who is the "fifth student"), so must be Shirley. Also in the list in #5 is "the one who chose Virginia Woolf's To the Lighthouse"; that's not Ruth Yorke who chose AA, nor either of the men who chose Hemingway and Faulkner, so it's Ruth X. But wait!, Ruth X is the "fifth student" and we have a contradiction. So, unwinding, if Yorke chose "Absalom! Absalom!" then what the fifth student shares is Yorke's author, not Yorke's first name.
F. (Continuing the hypothesis from E.) In this case the "fifth student" chose the other Faulkner book, "Light in August". Now, where does Yorke appear in the list in #5? Not as "Ms. Underwood" (wrong surname) nor as "the only Valdez" (wrong surname) nor as "the person who chose TTL" (wrong book) nor as the "fifth student" (I take it the wording of #5 is meant to exclude cases where that student is the same person as the one they share whatever-it-is with); hence it's Oscar Yorke. Now, there's only one Yorke so (by B) our siblings are Ruth X and Peter X, and Peter chose "The Sun also Rises". But this is impossible, because from the list in #5 we have: Oscar Yorke (chose AA, hence not Peter X), Ms. Underwood (female, hence not Peter X), Valdez (only one of that surname, hence not Peter X), the person who chose "To the Lighthouse" (wrong book to be Peter X), and the fifth student (chose "Light in August", wrong book to be Peter X). So no one can be Peter X. So, unwinding, we have found that Yorke did not choose "Absalom! Absalom! and hence (by D) that Yorke chose "Ship of Fools".
G. OK, let's think more about Yorke. Yorke isn't either X (from B) because there is only one Yorke. Yorke is also not the man-who-isn't-an-X because he chose something by Faulkner (by B) but Yorke chose "Ship of Fools" (by F). So Yorke is either Ruth not-X or Shirley. Where does she fit into the list in #5? Not "Oscar" (wrong sex), nor "Ms. Underwood" (wrong surname), not "the only Valdez" (wrong surname), not "the one who chose TTL" (wrong book). So Yorke is the "fifth student".
H. What does Yorke, the fifth student, share with the person who chose "Absalom! Absalom!"? Not her surname (there is only one Yorke by #4) nor the author (Yorke chose Porter's "Ship of Fools"), hence her first name. The repeated first name is Ruth. So Ruth not-X is in fact Ruth Yorke; and the other Ruth -- who is Ruth X -- chose "Absalom! Absalom!" (So the not-X man who also chose Faulkner must have chosen "Light in August".)
I. Now, consider these three: Ruth X (Absalom! Absalom!), Oscar/Peter X (The Sun Also Rises), and Peter/Oscar not-X (Light in August). These must be the first three people in the list in #5, because the other two are known to have chosen other books: "the one who chose TTL" and the fifth student, who (by F,G) chose "Ship of Fools"). Two of these three are men, which means that Ms. Underwood must be Ruth X. So X = Underwood; Peter is Valdez; and Oscar is the other Underwood.
J. The remaining student -- the fourth in the list in #5 -- must therefore be Shirley Zaniewski.
So the final line-up is:
Oscar Underwood Hemingway The Sun Also Rises "Oscar"
Ruth Underwood Faulkner Absalom! Absalom! "Ms. Underwood"
Peter Valdez Faulkner Light in August "Valdez"
Shirley Zaniewski Woolf To the Lighthouse "one who chose TTL"
Ruth Yorke Porter Ship of Fools "fifth student"
and unless I have erred, all the given conditions hold as required.