As for Barnabas and Jeff, and Barnabas backing down, first, Barnabas would never have gotten into a fistfight with Burke. Barnabas's confidence came from the supernatural tricks he had at his disposal. Second, someone who's been leading a pretty sick, irresponsible, weaselly existence up until very recently (vampire), who before could defeat anyone easily, would get spooked down to his bones at the loss of those powers. He couldn't possibly have the same confidence as before.
Barnabas just recently chose to give up all his plans to spare Jeff Clark's life. That was a pivotal moment in Barnabas's life. Clark doesn't know, and gets confrontational.... That's a pretty crazy, complicated situation, where there's no sensible way available to react. Do you try to beat up a rival whose life you just spared.... because he doesn't appreciate it? Because you're losing what you care about most to a clueless jerk? Or is Jeff the symbol of Barnabas's new morality, someone he needs to care about because he makes Vicki happy?
Man, am I overthinking this.......
Gothick.... Yes, I agree, if it comes to bodyswapping for love, I think you say no, no matter what.... and he did. The insanity and absurdity of the whole thing may have helped him a lot in making the decision to "cry enough". The idea of escaping Ang kept him thinking about it, though.