Perhaps it was easier 70 years ago with large families, I am youngest of 12 and certified ADHD. Older siblings do set role models and in a crowded one bathroom home and six older sisters patience and frustration tolerance was a necessity learned early in life. Also entertainment almost always involved interacting with older children unless you went outside and joined others your age who did not return to play.if your social skills were to edgy. TV (eventually)
was a family affair and youngest seldom chose the program.
I am not recommending larger families but perhaps pleasantinteresting activities involving many similar aged children and teambuilding might be helpful. I am as far from an expert as one can be so iam seeking opinions not suggesting advice.
PS many(but not all) of the Residual behavioral issues were solved at a military school/ Basic training facility at age 16 Apparently that doesnt work for all.