These examples could all be correct, but the subtle differences, if any, are given below. Is there someone else? I thought you only liked me! I'm worried that you have another girfriend. Is there anyone else? Who else is coming for dinner besides you? Would you like to have something else? Do you like this gift or do you want something else? Would you like to have anything else? You ordered a hamburger and soda, but do you want anything else, or is that enough?

Both are correct but if you use anyone or anything, the answer may be plural.

They're all correct! Usually anyone and anything go in questions, but these questions are fine with someone and something.

Oh, I understand your question now. In negative statements, only use "anyone," "anything," etc. There are situations when "some-" is OK but the rule is true 90% of the time. I don't know anyone in this city. I haven't eaten anything all day! In questions and affirmative statements, both "some-" and "any-" pronouns are OK, but sometimes the meaning changes. This is because "someone" means "some one person," but "anyone" means "any person or people at all." (Same for something and anything.) For example: He dates SOMEONE who has blonde hair. (= He has one girlfriend. I don't know her name but she has blonde hair.) He dates ANYONE who has blonde hair. (= He may have zero, one, or many girlfriends but he will only date blondes. Even if she is old, ugly, mean, etc. he will date her if she is blonde.)