Orm and Arthur’s feud was mainly rooted in the death of their mother, who Orm later learned was still alive. The brothers still had their other differences, of course, but with Atlanna alive and Arthur sparing Orm’s life, it’s possible that Ocean Master could mellow out a bit in prison. After all, the two weren’t always on bad terms in the comics, and there were even times Arthur deferred rule of Atlantis to him.
Article source: https://www.cinemablend.com/news/2464237/6-great-comic-directions-aquaman-2-could-go-in