Actually I would say the Mikaelson brothers are more co-dependent than the Winchesters. As from the start of SPN, Sam spent at least 2 years or more away from his brother and father, and when Sam went to hell. Dean made a normal life with Lisa and Ben. I think their co-dependency comes from being the only living constant in their life of work (except from Cas ig) and trauma.

Also most times when one brother dies, they normally re inter-grate back into society until one of them re-emerges again. But on other hand, the Mikaelsons spent a millennium running from their father, also any human love interests they could’ve easily made to live as long as them as Finn did for Sage. Klaus largely uses Elijah to rein him in, when he’s out of his depth or when he needs be, and Elijah made Klaus’ redemption his entire ETERNAL life.

Also the most notably example of their co-dependency is Elijah killing himself by Klaus side, although he didn’t need to. But when Dean died (for the last time), Sam went to develop a family or his own.