Sorry to hear about loss of your brother. It would likely be easier to find someone local with the skills and tools if you just want to get it running without taking up a new hobby dealing with antique programming.

Read a copy ECUs EEPROM file (not the flash .bin) using nefmoto flasher.
Then, use eeprom tool
http://nefariousmotorsports.com/forum/index.php?topic=6134.0
to set the immo off and then fix checksum within the revised file. Note that eeprom tool can be used as standalone command line program or it is even easier to use together with the visual logger GUI if you get that setup.

Once you have the EEPROM file ready, then you will need to use a bench-flash cable to flash it directly back to the ECU in boot mode (not via the cars OBD port!). There are plenty of tutorials explaining how to access boot mode so read up on those first.

Alternately, if you get the clusters SKC, you can use that along with full VCDS (not lite version) to adapt the new ECU without disabling immo following VCDS directions.

Thank you very much for your answer!!! I'm a bit slower than I used to be since the stroke I had.
       Since I already have an identical spare ECU ( 4Z7 907 551 AA out of a 2004 A6 2.7T S-Line  ), I just have to find a way to get the SKC numbers for each of the 2 ECUs.