I would like to express my thanks to all of the people that have responded to my Oracle query and have showed me the way ... :-)
I was not aware of the Oracle SID which makes things much more easier to implement. As many of you mentioned it looks like I only need one oracle account on each server I want Oracle to run on and then 'share' this account amongst all of the database instances setting the proper environment based on the SID.
Many thanks, George