How do I run a method from a relative ViewModel and get its return value?

To better show my problem, I drew a graph of how my ViewModel hierarchy looks like so far:

What I want to achieve is simply call a method from ScriptEditorViewModel and ask it, if the object, which is currently being edited inside EditObjectViewModel has been specified in the script. Later I also want to send some information to ScriptEditorViewModel and make it generate a script for the object if it doesn't exist.

ScriptEditorViewModel and ProjectManagementViewModel are 2 separate tabs in my program, which are basically operating at the same time.

Is it possible to do that and if so, is it a good approach?

Note: I'm currently using ReactiveUI as my MVVM framework but any other MVVM solution is also welcome.

Solution

When using MVVM pattern, you want to decouple components.

In View part there is xaml with bindings to data and command present in ViewModel.
In ViewModel you should keep data that is presented and logic that does something with that data. It is not the wisest thing to couple multiple ViewModels - keep their logic separated. If you have a command method, all data it deals with should be present in its ViewModel. For anything more complex, you shoud consider communicating with some kind of service or database.
Hence comes the Model part. Here you want to create the model of something you want to store and not necessary present in a View.

I don't know if I understood your problem well, but including a database or any kind of 'persistence layer' into your solution should resolve the problem of accessing specific information. You can create some in-memory storage for start.