help flaring nickel-copper lines

What kind of tool are you using? This is not the tool to go el-cheapo on. Get a professional double flaring kit, Mac, Matco, Snap-On, etc...

You have to use the tool provided in the kit to set the amount of tube to stick out past the flare tool for the first flare. Make sure to crank the f*ck down real tight on the clamping screws/wingnuts for the clamp tool - you must have the tube securely held so it doesn't walk when trying to flare.

Then use the round tool in the end for the first flare.

And remove the round tool and finish the flare.

*Note: The harder the metal that you try to flare, the tighter you have to clamp it...