SQL SSIS Closing Files already in use
When an application opens a file, it specifies what type of access is allowed by concurrent processes (none, read, read/write, etc.). SSIS cannot change that. The file must either be closed or the other process terminated. 

Although you could programmatically identify the terminate local processes owning a file handle, that can be challenging with remote processes and/or UNC paths. Personally, I wouldn't go there. A better solution is to have users copy files to a staging location once they are ready and have the ETL process them up from there.