Yup, if you're going to be in that situation, Sera, Blackwall and Viv are pretty much the ideal team for it.
I had Dorian, Sera, Cass, and 2H Warrior.
My strategy was:
Dorian does barriers and revives
2H Quizzie & Cass war cry/charging bull immediately to build guard and then whack away, building guard every chance they can, Dorian barrier-ing them when their guard goes down.
Sera actually takes care of herself pretty well, her AI is decent at using stealth + evading. just have to bring her back, and sometimes micromanaged her to get her leaping shots at the right time. I imagine Varric is pretty good at this too, if you have Cole, you'll definitely have to babysit him too, but he'll do higher damage most likely. If that doesn't work out, it may just be best to let him be dead and focus on mages + tanks.
It took me a few tries because at first I got impatient and wasn't micromanaging enough, but then I realized how much faster it would go even though it would take longer to do.
It is really obnoxious, but it is totally possible. And I actually learned more about the combat system and how to use characters/tac cam effectively in that one battle than I did any other situation, so I'm glad I did it.