hey john. Don't cut the line! try this first. Get a VERY small pipe wrench, the smallest I could find is about 6" long, may not be available locally, but they ARE out there. That will FOR SURE get that fitting loose. then, unless the fitting is frozen to the line, you are good to go. Upon reassembly, put some copper anti seize on the line, so it will never seize the fitting. If things are too far gone for this, then you have no choice but to make up a new line, not that big a deal , really.
Yes, one of the fittings is 1/2", the other is 7/16" . If they are ok, use what is called a "line" wrench, aka, flared end wrech. good luck, gz