How to maintain interactions among separate assembly-windows?

How to maintain interactions among separate assembly-windows?

I have an application in which a MainWindow and its associated C#
code-behind and ViewModel exist. There are four separate and independent
assemblies whose windows all need talk to the MainWindow but cannot. After
failing to using VS 2012 IDE for inter-assembly window talks by using
project dependencies and project build order, I've consulted the book:C#
5.0 in a Nutshell, Fifth Edition by Joseph Albahari and Ben Albahari for
info on loading assemblies and packing a single-file executable. My hunch
is that inter-assembly window talks won't happen until and unless separate
and independent assemblies be somehow "linked" together either by means of
tweaking the XAML mark-up or the code-behind or both, or else by
completion of a single-file executable. Is this assessment correct? Are
there more efficient way to do the same than these? Please help.
I think VS is misleading when I set both the project dependencies and
project build order correctly, the main window cannot even find the
existence of any of the auxiliary windows, let alone communication
opportunity. The "build" operation does not build for a single solution or
a single-file executable with three *.DLL as it should. They remain
isolated and refuse to be inter-connected.