Some of those hoses can be a real bear in that manifold block. Open end wrenches tend to round off the fitting and most flare wrenches won't slide on.
Good Vice-Grips can loosen the fitting. Don't worry about damaging the hose, you're replacing it anyway.
If worst comes to worse, cut the hose/fitting between the crimp sleeve and the brass flats. Then use a 6 point socket.