I have 2 solutions in Visual Sudio, one is a Unity project and the it is a solution with common controls and common resources and styles, all in only one project inside solution. Then, that solution added in Unity by package manager. Well, In that solution of components, I have added 2 more projects in Visual studio.
One of those projects is referenced in another and if I compile and execute this solution by Visual Studio,its ok. This is work.
The problem is when execute this in Unity. Unity throws many errors about it cant find these projects refences
How can I add theses references in Unity?

PD.: If I have all file in one project, everything is Ok and Unity works but I dont like to have all file in only one project

Right now, I have 2 solutions, one is a Unity project with many projects inside solution, this is work. And the other solution is a Visual Studio project with common control and other common views and I have only one project in solution (called NoesisProject-blend) and it works fine but now, I have added 2 New projects in this solution and when I update package by package manage in Unity, Unity crashes because doesnt find references these 2 new projects.

The error in Unity is: The type or namespace name `XXXXX’ could not be found. Are you missing a using directive or an assembly reference?

And my question is how can I reference in Unity these new projects? By assemblies or something?

I have attached the images

PD.: Each project in the solution it is a different assembly (different dll file)

Yes, that was my problem. I did not define the assembly definitions in Unity.
Thank you