can these boards be programmed by another UNO much the same as a UNO can be used to program a NANO?
Yes, as I already said in your other thread:http://forum.arduino.cc/index.php?topic=577745You could also connect a USB to TTL serial adapter to pins 0 and 1 to continue programming the boards over serial. The advantage is that you will also be able to use this connection for serial communication with your computer, debug output for example.Of course, none of that will work if there was a "magic smoke" incident that destroyed the ATmega328P in addition to the CH340.
FTDI|Uno----|----RX|TXTX|RXVCC|5VGND|GNDIf you are powering the Uno separately then don't connect the VCC pin.If your FTDI adapter has configurable power levels, make sure it's set to 5 V.The above connections will not provide an auto-reset circuit so you will need to press the reset button on the Uno at just the right time in the upload (just as the upload starts but after compilation is finished. You can turn on verbose output during upload in File > Preferences to get an idea of the progress of the upload. If you want the auto-reset behavior like when you used the Uno normally, then you need to connect the DTR pin on the FTDI to the reset pin on the Uno via a 0.1 uF capacitor.