It's only possible to reference one dll at a time, so what you are trying can only be achieved by matching the namespace of all your dll's to one and the same namespace. this way you can use one include. so for instance you change all namespaces to MyCompany.BaseNameSpace you can include like this:
using MyCompany.BaseNameSpace;
I personally don't see why you would want to, your libraries are separate for a reason right? So I recommend adding them and including them separate as well.