Currently I have everything set up within a file geodatabase but I want to be able to edit offline. Do I need an enterprise database instead? This would also be beneficial for if multiple people wanted to edit it, yes?
You will need an Enterprise Geodatabase, use the ArcGIS Data Store, or create an ArcGIS Online hosted feature service. Unfortunately, you cannot create a feature service from data residing in a File Geodatabase.
My data is now hosted as a feature service on ArcGIS online. How do I change the settings to make it editable offline? Or since that data was originally from a file GDB, it won't work anyway??
You will need to enable sync on the service. See the section Allow offline editing or collaboration in the below link:
Manage hosted feature layers—ArcGIS Online Help | ArcGIS
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