The main difference is that generally “还是” is used in questions, and “或者” is used in statements. The translation of “或者” is ‘either…or…’, whereas the translation of “还是 ” is often just ‘or’.
“是不是”一般用在谓语前面,也可以用在句首或者句尾。 If one raises a question and is somehow certain about a fact or situation, they can use this kind of question to confirm their guess.