I'm in way over my head.

So I just beat Rome and I had to use a quartz to revive for every fight on the last area. I think the difficult level was 25 and my strongest character is my Archer at level 20. The rest of my team are all around level 10.

I've been relying a lot on a level 50 beserker support, but that's coming back to bite me in the ass. What should/can I do to catch up to where I'm supposed to be at this point?