Can't empty trash or move items out of trash

I have an external G Drive where I do my Time Machine back ups. It has become full and TM isn't deleting the oldest back ups to make room for new back ups.

So I took it upon myself to grab 21 of the oldest back ups and drag them to the trash. Upon selecting empty trash I get a can't be emptied - it is in use by the hard drive. No back ups are running so don't know where it is tied up.

I tried starting in safe mode, but the G drive will not appear on the desktop. So I restarted and tried to move the items out of the trash to a new folder on the hard drive. External folders transfer but no internal files do.

I am stumped. Short of use the disk manager to erase the whole drive, not sure what to do.

Any idea how to resolve this?

Thanks