Yes, you can share someone's story in many cases. For example, if the person has given you explicit permission to share their story, it is completely fine. Also, if the story is in the public domain or is a matter of public interest and you are sharing it in an appropriate and respectful way, it can be shared.
It depends. If the story is in the public domain or if you have obtained the proper permission from the person, then you can share it. However, if it's a private story and you share it without consent, it could be unethical and in some cases, illegal.
Well, in most cases, if the Instagram user has not set any restrictions on their story sharing, you are allowed to share it. But keep in mind that some people might not like their stories being shared without permission even if the settings allow it, so it's always polite to ask first. Also, if there are any copyright or intellectual property issues involved, that could be a problem too.
Well, first make sure you have the person's consent. Then, you could tell it orally to a group of people, or create a blog post about it. Or, if it's suitable, turn it into a video and upload it to a platform like YouTube.