aah, thats a different problem to the one I thought you were originally describing.

You need to bring the smaller datafiles up to the size of the original as much as possible. If space prevents this and these files are very small, get a drive that allows you to create new files of a decent size, shrink the small files with the emptyfile option to empty them, then drop them.

at the end rebuild the clustered indexes on the tables in the filegroup and SQL will attempt to spread the data between the datafiles.

I see no need at all to remove all your data from the database and reload it but you will need an outage and back the database up first.

If you can restore the database to a test server first to practice the task, script it up and get timings.