Yes, you can. Instagram usually allows sharing others' stories if the person's settings permit it.
Yes, it's possible. However, it's crucial to note that the ability to share someone else's Instagram story to your own depends on the owner of that story having enabled the sharing feature. If they haven't, you won't be able to share it.
In most cases, you can. But it depends on the privacy settings set by the person who originally posted the story. If they have allowed sharing, then you'll have the option to do so.