A VM residing on the Datastore has 4 snapshot files with 550 Gig each.
Is this the command's output for the VM that you've mentioned in your initial post? Where did you see the "550 Gig each"?
According to the file listing, which you've posted, the VM has 3 virtual disk. Each of them is "thick provisioned" (128GB, 100GB, 150GB).
In that case you won't need much additional disk space on the datastore when you run "Delete All" from the snapshot manager, because the base disk has already been fully provisioned, and will not grow in size. So with 300GB free disk space for a helper snapshot (which will be created when you delete the snapshots while the VM is powered on) , it should save to run the "Delete All" job.
Please note however, that deleting the snapshots may take considerable time due to the snapshots' sizes. So please remain patient.
André