It is possible that his behavior is very different with one parent than the other. The worse behavior often means the child feels more safe with you.
My favorite approach to aggression — and one I’ve seen work time and time again — is Ross Greene’s CPS model:
https://www.additudemag.com/category/parenting-adhd-kids/behavior-discipline/oppositional-behavior/
I highly recommend his books “The Explosive Child,” and “Raising Human Beings.”
Penny
ADDitude Community Moderator, Parenting ADHD Trainer & Author, Mom to teen w/ ADHD, LDs, and autism