I would have agreed this in other situations. But sadly I have to disagree with you here. Because that man had leave child with mc who was young himself. If Mc wanted he would have also leave that child with his dad when he decided to run away from home. But he didn't. Mind you both the child father and mc didn't had anything with them. Yet Mc took the risk.. He took that kid with him. He Raised Him. Just that man giving birth to the child and being biologically doesn't mean a thing I say. I mean even in real life, if this happen then I think most people will choose the who made what they are today. Blood related or not. That kid wants his brother because he had seen what his brother done for him. He saw how much he loves him. And how can never leave him behind. So yeah
The father left because he was a coward and thought he couldn't do anything for his child, just like how the mc gave up this time because he thought the kid would have a better life with his father since he has a stable job and life than him, he even *almost* k!ll himself with the child in the ocean lol wonder what will happen if the ml didn't stop him?? anw, they were both in a worse situation when the kid was just a baby, and i know that the father should've helped with raising him, still, i think they all just have to have each other's back this time. This kind of thing happened in all fictional stories, it is annoying and seems undeserving for the father, but given the fact that he looked for his kid, he still cares, just not enough to come back much earlier. So anyways, this is some of what i think lol. They have to have a discussion, not just suddenly changing the child's environment.
The three/four of them should have a talk about a somekind of situation they should take. Like the kid will be with his father every 2 or 3 days or smth. I mean, i know the father came too late, though the kid is still a kid, but atleast he is trying to be a father, no? Given that the kid is in school and looks well except for the fact that he misses his bro. But yeah, they shouldn't just take him far from his brother like that. Maybe he'll want to be with his father too but it'll take some time fr.