Do you use System Restore now and then? If yes, it is probably responsible
for creating the *(2).dll files. You're seeing the rule of one unique name
per file in any one folder in action. A restore point might encompass files
that have since been changed due to updates or software installations.
Instead of overwriting the existing file, a new name (filename(2)) is
created so that both are on hand.

If you are not pressed for space, leave the "extras" in place so that they
are available for undo operations with System Restore.

As for which file is the working copy, it would be the one without the (2).
A program's instructions will be looking for the original names, not the
altered names.  

If a program pops up an error referring to one of these duo-named files,
then this would be another situation where it would be helpful to have the
(2) file still in existence. Rename the pair of files so that the (2) file
becomes the working copy. Or reinstall the program so that it has the exact
file version in place that it needs.