Hi,
Thanks for detailing me, your explanation is very good which made me know many things & ultimately led me to the resolution of mine tnsnames issue. And now I got the desire result i.e. now I am able to start my DR SAP PRD system (R3trans results 0) and also able to do tnsping as per the guide ( which was the first step for me)
I reverted tnsnames.ora to its original state at /sapmnt/PRD/profile/oracle and only maintained tnsnames.ora at /oracle/PRD/11203/network/admin. And now everything is working fine as they should.
However there is one concern related to listener.ora file, if we check in guide there is one line as GLOBAL_DBNAME=o11_south_DGMGRL (page no. 15) which is conflicting as per Annexure there it is mentioned as GLOBAL_DBNAME=o11_oracle-vm2_DGMGRL (page no. 56).
Can you figure it out which is correct one
For now I have kept GLOBAL_DBNAME=o11_south_DGMGRL / prd_standby_DGMGRL
As of now my DR server is ready with DB parameters & SQL*NET configuration, now I will do the same on my PRD system and then will move for DB restore.
Thanks once again. Your post made my day 
Regards,
Kiraang.