Diplo Bluff and Inti
WHich one is more useful in your opinion?

I think it depends on your role playing style. My main character is a fighter/warlock, and so has Intimidate, but I can't bring myself to be mean to people, and so it's a bit wasted.

can my party characters use their talk skills as well? for ex, one of my fighters will talk in intimidate and i will speak diplomatic? or only protagonaist