Aziraphale and Crowley 'kinda' adopt a young Hob Gadling when his family gets wipped out by plague/war/famine. And share custody while he grows and they continue to get their own personal sh*t together.
In his mid 30s, Death turns up with a request for him to be a friend/ share some of that family love for life and humanity with her little brother. Possibly don't mention the angel, demon legal gaurdian thing just yet though. Here's the plan.
Cue a complete shift in power dynamics where Hob knows all about the supernatural world and who Dream is. He's just waiting for the right moment to tell him. He was going to in 1889 but that did not go as planned. Aziraphale and Crowley remain alarmingly concerned about the entire thing but are good supportive dad types.
When Dream gets captured Hob comes to the rescue with a whole host of Gaimon verse back up. With a, 'Surprise! Please don't smite my parents. Tah, love you.'
