For instance: Two potential defendants who are in custody have already been arraigned and/or requested an attorney. While they are still in custody, I wish to talk with them on un-related offenses for which they have not been charged or arraigned. Is their previous arraignment and/or attorney request "case specific", or can I talk to them without the arraignment or attorney request being an issue.

The constitutional right to an attorney is offense specific.

But remember, if the defendants invoke their right to counsel during custodial interrogation the Fifth Amendment applies, which is not offense specific.

JAS