I don't quite remember who the author and title of the story but I can remember a little bit about the story:
1. The twin brother and sister of the future come to the past to meet with Dean and Castiel, they are being chased by their older sister who has been kidnapped since childhood. The twin was the son of Dean and Castiel and they want to change the future. I read it in FF and this story have a sequel.
2. Dean befriend with Jimmy Novak, Jimmy has a twin brother named Castiel Novak. Their father always mistreat them. Then Jimmy died in an accident. John Winchester knew the abuse and threatened Zachariah. I read it on AO3 and I can't found it again.

Not a lot information but I'm hoping it's enough for someone to recognize it. Thank you very much for your help.