The first pic you sent shows the brake hose which goes through the upper crossmember. The "C-clip" is indeed all that holds it in, BUT, you have to break loose the line that goes into the other side which, as I recall, is that "nut" you are seeing where the steel brake line goes into. Use a wrench on it to hold it in place and then turn out the fitting on the steel line. Then knock out the "C-clip" and pull the hose out.
My experience is that you may have trouble undoing that steel brake line from the rubber hose. Put a little penetrating oil, Liquid Wrench/PB Blaste etc., on the fitting and line and let it stand a while. Typically an open end wrench will round off the fitting. They make wrenches specific for steel lines which looks like a six-point box wrench with a cut into it to slip over the steel line called a Flare Nut Wrench - photo enclosed. These work better than an open box wrench.
However, if the fitting is really corroded, these too can round off the fitting. Next up is Vise-Grips. I typically clamp the Vice-Grips tight enough so as not to spin on the fitting nor tight enough to crush the fitting. Give it turn or work the fitting slightly left/right to break it loose. Vice-Grips will do the job for sure, but you may destroy the nut and I suspect at this point the line is corroded and frozen into the fitting and you are going to spin/twist the brake line off. If the line does twist off, then a new line will be in order unless you have the tools to splice in a section of steel brake line.
The fitting down at the bottom of the hose that attaches to the rear end is part of the hose - second photo. Looking at your picks, I would recommend replacing the rubber line and getting all new steel lines - while its out, I would rebuild the rear brakes if they have not already been done IF you are not replacing the rearend with something else.
I would not bother to undo the steel lines, just replace them with the rearend out with either pre-bent lines or do it yourself if you have the tools to do so.
Dropping the rear is pretty straight forward once you get the hose line undone. Once the rear is out, I would suggest installing new control arm bushings/bolts. If you wanted to go even further, and finances can be justified, I would add the boxed lower control arms and a rear sway bar for a little additional handling. Price out the new bushings and labor at a shop to install and it might be easier/cost effective to just go with new boxed lower control arms for now and then later install a rear sway bar.