I actually have found that Craftsman flare nut wrenches, though not bad, aren't quite good enough. I recommend S-K tools, which you can find at some auto parts stores. There may be others as good, but I have not seen better. The tiny margin of extra tightness and rigidity can make the difference between success and failure on a rusted fitting. They're silly expensive and worth every cent.
There may be enough slack in the lines to re-flare, but remember that these are double-flares, not that easy to do, especially in place and on old lines. It can also be difficult to get the new nut far enough down on an old line to make room for the flare fitting clamp. By the time you've spent the money on the double flare tool and the time on making it work, you might be better off getting a new length of line. As an alternative, you could cut the line a little further back, give yourself some room to do a good double flare, and then use a coupling to add a new length between that and the MC.
As 8Mud notes, Here in rust country, even when you get the fitting loose it doesn't guarantee that the fitting isn't so seized to the line that it will just twist it apart. You can sometimes coax it loose by wiggling back and forth, etc. When it's clear that the line is toast anyway, I usually cut it off flush at the fitting and use a 6 point socket wrench to remove the fitting.
