Let's start with the "Two or more objects..." error messages. When those go away, we can look at the unrecoverable build error.
Basically, that error is saying that your setup is authored so there are files in the same folder with the same name. Usually, you can double-click on the error message and it will take you to one of them.
One way that can happen is if you add Project Output Groups from multiple projects that have the same dependencies. You can get multiple copies of the dependencies that way. If you go to the folder that has the multiple files, you should be able to select a copy and exclude them... or try the detected dependencies folder.
Some ways you can track this down would be to select an assembly and go to the property grid and open teh "dependencies" object. This way you can see which dependencies an assembly is bringing in. You can also go to a Project Output Group and check the "dependencies" properties or the "outputs" property, which lists the files in the project output group.
Really, once you figure out why you have multiple files of the same name in the same folder, we can find the best way to clean it up.
Good luck, hope this helps.