Specific sick dean fics
1st One:dean and sam werent brothers,mary worked at a haospital as a nurse where a young lady gave birth early and then escaped leaving the baby which was born very weak and expected to die but mary beleived in him and john amd her adopted him and later came sammy.(bobby was dean's real father and he and john never got along)
2nd one:mary gave birth to dean but he was very weak and had a lot of problems and her father wanted to give his grandson his familey name but when he saw dean he refused as he saw that dean wont make it but when sam was born he wanted to give him his name as he was healthy but mary screamed at him and refused but in the sequel to this story he regretted that and wanted to be a part of his grandsons' lives
they are both on fanfiction.com if that helps
i hope someone finds them they are amazing stories
i think both are considered au ..i dont remember if they were still hunters or not