I'm in favour of disguising Kelaeon and maybe Sharka as Sith. The Prison Officials might not be as quick to question the motives of a big scary Dark Lord who requests access to the prison. People who talk back tend to get eviscerated. Sairen's also a good liar/great intimidator, so I could make it work.
edit: Or...make Sairen and Kelaeon the Sith. I'd do the talking and he'd look menacing/force grip any insolent guards.
I find it amusing that Darth Zairon is listed under Kel's enemies. I was almost his minion.