What investment?
Sershow: "I heard about your business. But have you considered what would happen if we blockade your port? But if you let us use your port to ship grain to the East, it's cool".
Gallahan: "Sure. Pay me some docking fee."
The Lombardi before anything else are businessmen. That's what they're known for even if the grandfather has some political standing. I mean unless Sershow is smuggling military arms to enemies or exporting drugs. I'm pretty sure there's no downside to allowing him to use their port.