Have I missed something? If Dean and Mick are bruvvas, and Shirley is now Mick's mum and not his sister, who is the dad??? And why was it all made to look like they were siblings, why wasn't Shirley just a teen mum or whatever? I don't understand!
Remember the bloke who Shirley was shacked up with in the caravan after she shot Phil? Buster or Spike or something? Well Dean sussed he was his (Dean's) dad. As he was leaving, Buster/spike/whatever made some veiled comment to also being Mick's dad.
Shirley revealed to Phil months ago that her and her mum had buggered off to the family caravan early in the pregnancy and didn't come back till after Mick was born. They let everybody believe, including Stan, that Mick was Stan and their mum's child.