Halfway through replacing the clutch slave cylinder, with significant assistance from the info on here

Early style, so metal hose from slave (which is rusted to hell), flexi to chassis & union onto forward steel pipe. Got the old cylinder off, new one fitted, along with a very spangly new Brickwerks braided hose which (if I've understood correctly, replaces the flexi and the rusted metal pipe, and goes straight onto the main pipe under the chassis).
Have got stuck at the connection onto the forward steel pipe. I'm trying to work out which bit I unscrew from which bit! Hopefully the picture below should help. I'm guessing A is something to do with clipping to the bracket, so not important.
Am I right in thinking that C is the union on the steel pipe, and is the bit I want to hold still, and that B should unscrew from it, revealing a male thread on C that the Brickwerks pipe screws onto?

Whether I actually get them to unscrew is a different matter,as the spanner 'flats' aren't very flat, but want to ensure I'm attacking the right bits first.
Thanks in advance,
Rob & Sandy