You guys are making this fight harder than it has to be. Assuming you didn't already balls it up, then listen...
You know Eileen is going to fight Henryk. You know melee attacks might make Eileen hostile if you hit her on accident... So... What's the next logical step? Use your pistol. That's it. Time your shots to parry him. He'll be focused on Eileen the whole time, you don't have to dodge, or roll, or do anything else... Just shoot him, and go in for a visceral if you can.
I got a few melee hits in before Eileen showed up. She got there, I backed off and just offered support by parrying his attacks with my pistol. He died in literally seconds.
It's not hard guys. Just plan ahead.