아니요 and 아니오 is completely different. You can't interchange them. Although pronunciation is similar but, you have to watch out when you are writing in Korean.
아니요 is 아니 + 요. In this case, 아니 is an exclamation, and 요 is postposition for polite form.
아니오 is 아니 + 오. In this case, 아니 is a adjective, and 오 is a suffix for ending. So, there is no polite meaning.
When someone is asking you, you can answer with 아니요, becasue yes or no form is 예/아니요. But you can't use 아니오.
When you explain something, you can end the sentence with 아니오.
e.g.) Panda is not a bear. => 판다는 곰이 아니오. (o) // 판다는 곰이 아니요 (x)
아니야 is 아니 + 야. This 아니 is similar meaning with 아니요's 아니. And this is most informal form. (It can be distinguished with suffix 야.) So, you should only use this word with your close friends. Moreover, if you talk with your friends, you can use the basic form 아니 as well.