Yes, some of them do, including Hedwig.
No Harry Potter doesn't have any sibling's.
Harry Potter does not have any brothers or sisters.
Yes, several. Fred Weasley Remus Lupin Nymphadora Tonks Dobby Mad-Eye Moody and Colin Creevy
No, only the Basilisk in Harry Potter is in the second book/movie Harry Potter and the Chamber of Secrets.
There is no janitor in Harry Potter at any time.
Harry Potter will appear in the Harry Potter books. If he was to appear in any other published novel it would violate copyright.
No, nor was she in any of the Harry Potter movies.
No, Toby Hemingway is not in any of the Harry Potter films.
No, owls cannot talk. Even in Harry Potter.
J.K. Rowling did not write anything before the Harry Potter series. She would occasionally write short stories that she shared with family and friends but she didn't have any published works until Harry Potter and the Sorcerer's Stone. Actually she got the idea to write Harry Potter one day when the train she was on had a four-hour delay.
There won't be any more Harry Potter books.
There were never any signs that Luna had any romantic feelings toward Harry. They were always good friends. Harry made it very clear that he was taking her to Slughorn's party as friends - which Luna in no way objected to.