Cannot delete time machine backups using terminal commands

+1 Please let Time Machine do its job of getting rid of old backups in order to free up space. Trying to do this using Terminal or manually will normally result in a ruined Time Machine External Hard Disk that needs to be reformatted and you will need to start over. In short, please leave it alone.

It is a very bad idea to mess around trying to delete Time Machine backups.

If your Time Machine backup drive is full, then there are two options.

1. erase the drive and start over with new backups.
2. replace the drive with a larger one.

+1 That has nothing to do with your Time Machine backups.

For that you need to see > Free up storage space - Apple Support

Yes, the best method of freeing up space on a Mac is to move large libraries such as photo libraries, music libraries, movie libraries to an External Hard Disk. Doing this is pretty simple but first it requires another External Hard Disk to move them to.

After you have gotten an External Hard Disk, locate the libraries on your MB's internal drive and copy them to the External Hard Disk. To teach the apps that use the libraries where the libraries now reside simply double click the library on the External Hard Disk and that will launch (and "teach") the app where the library now resides. Once you have done that you can delete the library from the MB's internal drive and empty the Trash.

Apple gives examples of how to do this in Move your Photos library to save space on your Mac - Apple Support

the same works for your Music and Movies libraries.