The flare nut on brake tubing is made of steel not brass. If you have brass,someone along the way has changed it.
3/16 tubing flare nuts require a 3/8 wrench & not a 7/16. Except sometimes the OEM will use a different nut to avoid mixing up lines.
If you are going to replace the piece of tubing, cut it off close to the nut & then use a ' good' 6 point socket or 6 point box wrench to remove it.
Yes, in some cases tubing can be flared while on the vehicle but it does require a good amount of space to do it. And some experince in using a flareing tool.
Compession type fittings are not legal for use on a HYD brake system in PA & even if they were I would never use them myself.
Keep in mind it doesn't have to be an exact match to the OEM one with that tight bend etc. Just need to get fluid from 'A to B' without kinks or leaks.
If you buy a pre-made piece of line it may have one nut longer than the other. The longer nut is for use in a wheel cyl. or something where the seat is set deep. Maybe in your case the hose end.
Off subject, if you do a M/C again, leave the mounting nuts as loose as possible so you can move it around. Once you have the lines finger tight, tighten the M/C mounting nuts then the lines using a wrench.