Brothers Evan and Adam Stuart grew up to be construction workers beholden to a Don for their right to work prime assignments in a mob town. That's where their similarity ends.
Evan is a river construction diver with a specialty in building bridges. Adam works high steel with a specialty in demolition. Evan is a Buddhist. Adam is a part-time mercenary. Evan is a pacifist. Adam is a contract killer.
The brothers courted the same woman, but Evan's passive ways cost him the love of his life. Sullen and bitter, time stopped for Evan when Adam married Gina…until a day ten years later when Evan arrived home to find the little girl who may or may not be his daughter waiting for him.
Evan's decade of stasis shatters. The new guy on his boat gets eaten, a change in mob royalty threatens his livelihood, and the Feds are pestering Evan to help them take down both his brother and the mob. The only thing that Evan cares about is making the most of his second chance with the girl who may or may not be his daughter. This time he's ready to fight anyone and everyone to keep the ones he loves, be they mobsters, killers, or agents of the government.
Diver Down is six months of Evan's first person observations as his he's challenged to rethink his values at every turn. Can he protect the ones he loves without turning into one of the monsters he despises?
If this is first person narrative, you'd do well to focus the hook on Evan. The way it reads now it sounds like the story has two lead characters. You give short shrift to the antagonist.
This story line is old old old. You're going to have to bring a new twist to it to hook my interest.