as per my understanding of ur question u want to set more than one sid in .bash_profile for multiple database instances .

there is no need in setting more than one SID in .bash_profile because first time u login to the operating system it will always point to one sid . to connect to the other database . u have to set the environment variables again . and login to the 2nd instance.

2nd option is create two different Linux login users and set two different sid's in different profiles.