Accounts and passwords are specified for the FILE not the table. Thus, if you are importing all your data into a single file, you need only set up accounts and passwords a single time on this single unified file. You can set up scripts that create and modify accounts in multiple files and this is often done, but that does not appear to be what you are creating here.
If you are importing data from individual file into a single unified file, you are only able to import the table, the relationships will have to be manually recreated in the new file anyway.
The existing relationships as recreated in the converted copies of your original single table files will only be of use to you if you don't merge all the individual files into a single unified file.