I have three files in trash that cannot be deleted

I have parallels on my BigSur MacBook Pro. Today I downloaded installers for High Sierra, Mojave and Catalina, then copied them on to a flash drive for archiving. I moved them to trash, but now I can't delete them. Here's what Ive tried:

• Empty Trash (I get "The operation can’t be completed because the item “Install macOS Mojave” is in use."
• Tried emptying Trash after booting in Safe Restart. Same issue
• Did a "Get info" on each file, and changed permissions to "Everybody :: read/write", but that hasn't helped.
• Tried launching terminal, then

$ cd /Users/<myid>/.Trash
$ ls -al (shows nothing)
$ sudo su -
$ cd /Users/<myid>/.Trashes
$ ls -al (shows nothing)

• If I <open terminal here> with one of the items in trash highlighted, I end up at

$ pwd
/Users/<myid>/.Trash/Install macOS Mojave.app
$ ls -al
total 0
drwxr-xrwx  3 root     wheel   96 Jan 24 09:23 .
drwx------  5 <myid>   staff  160 Jan 24 19:54 ..
drwxr-xr-x  3 root     wheel   96 Jan 24 19:54 Contents
$ rm -rf Contents                     # Get "Operation not permitted"
$ sudo rm -rf Contents                # Get "Operation not permitted"
$ cd ..                               # to /Users/<myid>/.Trash
$ lsof | grep -i "install macos"      # Returns nothing (no locks on files)
$ cd "

• I can't seem do anything with chown, chmod, either with or without sudo.

Not sure what I can do to remove these three installer files that are eating almost 20Gb from my drive.

Does anybody have any idea how I can get rid of them?