Problems Deleting Time Machine Backups

I made the mistake of manually moving super old backups (most from a laptop I no longer own, but some from this computer) from an external TimeMachine drive into my Mac's trash. When I tried to empty the trash, it deleted thousands of files but got down to the core files and they won't delete. I've learned from other boards that this was a massive mistake, but I need to figure out how to delete what remains in the trash bin.

When I attempt to delete each folder one-by-one, it prompts me to enter my computer's password, which I do. Then I get this error: "The operation can’t be completed because some items had to be skipped. For each item, choose File > Get Info, make sure “Locked” is deselected, and then check the Sharing & Permissions section. When you are sure the items are unlocked and not designated as Read Only or No Access, try again." I unlock it and the Sharing section has 3 files: "system - Read & Write," "wheel - Read only," and "everyone - Read only." When I attempt to change "wheel" and "everyone" to "Read & Write" I get an error that says I don't have permission to make the change.

Because most of the files did delete, I'm past the point of attempting to move them from the trash back onto the external drive - that doesn't seem to work. Any help would be really appreciated!!