I hit the Option button as directed before opening Bluetooth Preferences to delete old devices but only the one I'm currently using comes up, not the three other old ones listed under the Bluetooth menu.
How can I access and delete these?
I don't know who directed you to do it this way but the ⌥ method is for troubleshooting/removing active devices.
As far as I know, this is how you unpair/remove a Bluetooth device:
→ System Preferences → Bluetooth → Hover over the device you'd like to unpair/remove → click the
x to its right.