Part 5
Damian is a wizard now.
He was meant to go to Ilvermorny like every Amercian Wizard but since Harry was already enrolled in Hogwarts Bruce decided that Damian should be in the school too so they would stay together and protect each other.
They would both end up in Slytherin; only Damian would have fewer friends than Harry (Draco and Ron) and would mostly hang around Fang, and as a result, Hagrid. He will drag Harry into the forest every chance they get though.
Harry would immediately use the cloak once he gets it to help his brothers creature adventures even if they got into a lot of trouble for being out (not like he cares much when he's trying to figure out the stone deal). But also they have a bloody invisible cloak and will rub it in their older siblings' faces.
Damian tries to buy out the pet shop when they go to Diagon Alley. Harry helps in convincing Bruce they need every animal listed and a few that aren't. People don't like their pets at Hogwarts even if most of them weren't bought and are completely muggle (Alfred and Titus—yes, he is keeping his dog). Of course they still get Hedwig because she is the best owl.
They write to the others regularly. Damians are more like reports, and Harrys are more like postcards. Bruce needs like 7 plus letters from each of them to get the full story, especially since Harry is almost always in life-threatening situations that both boys have deemed normal.
Damian is a Muggleborn, btw, with no magical ancestors.
Also should mention here since it's not that much info for the Au, but since Harry grew up hearing his parents were drunks and left before a wizard could correct that, Harry is A-OK with adding Wayne to his name. Full name: Harry James Wayne-Potter, or Potter-Wayne. I don't know yet, but Bruce thought they should have his parents name like he did with Tim (I love that headcanon, shush).