For visceral back-attacks, you charge your attack, hit, they drop to one knee, then you just do a regular attack from behind, I don't even think you have to step forward, and you definitely do not have to move to their front. You can totally stick your hand through their spine

As for getting hit during a reposte, I don't recall that being an issue. You do have to shoot them during an attack animation, but you mostly only have to wait for their start-up for that attack, it doesn't have to be directly in your face. So you may have extremely good timing from the sound of it if you're waiting for the very last possible second and taking a hit. You should be fine shooting them a tad sooner to stagger them

Then again, pretty much everyone in the starting area are annoying until you get to a point in the game, or character strength where they don't matter. It's a great place to farm for bullets and vials. But I never tried to dazzle my way through much of that. I was more concerned about "parrying" the bigger fellas like knights and ogres

Also, for your Bloodstarved Beast parry positioning, are you using your dodge to move around the stage, and not just to dodge? Usually if you knock him down with a bullet, it means he was aiming to attack you, and there's a good chance you can dodge toward him a couple of times within the time frame to get the visceral on him. But you were co-opping so he may have been aiming to hit your partner. In solo it's almost guaranteed since you're the one he'd be coming after, he'd have to be within range to hit you, and aimed at you, so everything should be lined up and within distance