Reusing View Controller within Coordinator pattern

I have a flow (Flow A) of ViewController's in my iOS app. Flow A is rather complex (depending on circumstances, some view controllers are shown early, or not shown at all, etc.). In order to handle that I am using the coordinator pattern.

The code (simplified):

protocol Coordinator {
    func start()
}

protocol FlowACoordinatable {
    var coordinator: FlowACoordinator
}

class FlowACoordinator: Coordinator {

    private var navigationController: UINavigationController

    private var firstVC: FirstViewController
    private var secondVC: SecondViewController

    init(navigationController: UINavigationController) {
        self.navigationController = navigationController
    }

    func start() { ... }

    func present(_ viewController: (FlowACoordinatable & UIViewController)) {
        viewController.coordinator = self
        self.navigationController.pushViewController(viewController, animated: true)
    }

    ...
}

class FirstViewController: UIViewController, FlowACoordinatable {

    var coordinator: FlowACoordinator?

    func buttonTapped() {
        self.coordinator?.goToNextStep()
    }
}

....

FlowACoordinator contains logic about how and when to present view controller's using the present() method. So far so good.

Now I have a second flow, Flow B, mostly different from Flow A. Except I want to share a view controller between the two, let's call it SharedViewController. This is where things get strange, because I have no really good idea on how to share this view controller between the two.

The problem: I have a two way communication - the coordinator sets itself as the coordinator of the view controller it presents & the view controller calls methods on the coordinator as a response to user interaction. SharedViewController is managed by one of two Coordinators, though, and somehow it has to pass information to the current Coordinator, regardless of which one it is.

So far I found two solutions, both of them not satisfying:

1. An additional coordinator that handles just SharedViewController - this is a lot of overhead and largely defeats the purpose of Coordinators.

2. Implementing FlowACoordinatable, FlowBCoordinatable, ... in SharedViewController, and have multiple coordinator properties and call all of them at appropriate times. Also a lot of overhead, boilerplate code and calls to coordinators.

Any ideas on how to solve this nicely?