If you don't own the software, you can use the Revit 30-day trial to perform one-time batch conversions. Autodesk Viewer can view files, but it does not support exporting to DWG.
No – for complex, parametric, annotated families. rfa to dwg online convert hot
For large projects, many files, or where preserving complex family logic and parameters is required, use Revit itself or a desktop tool that supports Revit’s API. If you don't own the software, you can