just buy a spanner made from a unicorns horn......you will be able to get those nuts undone in no time, plus you have the advantage to tell ya mates you have a cop spanner
yeh last thing you want is for teh vice grips to slip and crush the brake pipe. When i undon mine one me car i just used a 13mm?? and a 10mm? (forget lol) and just gave it a quick tap with teh hammer....not a all my force hit just enough to break the seal.