re: "...When I try to loosen the two fittings, it just strips the brass nut...."

Speaking as someone who has worked on cars far older than yours (i.e., 240s), I've found that brake line fittings are notoriously prone to damage if it's done the wrong way.

That said (and believing that 240 lessons are applicable to your XC):
1) first rule is to generously pre-treat with PB-Blaster (a certain rust loosener) -- do not substitute with WD-40, silicone, or other pseudo-rust treatment.
2) use only quality tools, specifically flare-nut type wrenches (these provided more corners of grip than ordinary wrenches, and then only quality brands -- for this type of work, I only use Snap-On. Other brands such as Craftsman are notoriously imprecise, and (even in flare-nut style) slip somewhat!

An investment in just a couple of expensive, Snap-On flare-nut wrenches of the necessary size could have prevented heaps of aggravation and the need to replace more lines than you expected.

Check the 200-series archives for more. We have a lot more experience, simply because there are more of us caring for far, far older cars.

Hope this helped.