Hi, I'm sorry to say this is something we don't directly support yet: #1468
But there is still the possibility to implement and set your own resource providers that can understand a specific folder structure. For example, as explained here: viewtopic.php?f=3&t=1830#p10374
In the meantime I can think of having your custom provider to be able to find resources in more than one root, so you can configure it to look for files under FirtstDll/ and SecondDll/ folders, and that will allow the provider to find A.xaml and B.xaml. This is not the right solution though, because it won't work when using same file names in different folders, but maybe this is not your case now.