Before I break something: any tips on body to rear axle brake line connector removal?

Hopefully you're using the correct size line wrenches?
Once or twice I was able to shock one loose by using a short "cheater pipe" on the side I could reach.
This was after I'd heated it up.
I hit it hard and it came loose.
My last resort is a small pipe wrench, this will booger up the hex a little, hopefully you won't have to go to this extreme. Good luck! we've all been there.