Package A depends on C 1.0 and B depends on C 2.0. How much work it is to get down to one version of C in your dependencies is up to how different 1.0 & 2.0 is, and how A & B use it. But if you want them resolved, it's up to you to do the engineering to A or B.
Correct. The solution is to modify packages A and or B, which is a high cost approach (hence why FAANGs could throw warm bodies at it, but most everyone else throws their hands up in exasperation).
Package A depends on C 1.0 and B depends on C 2.0. How much work it is to get down to one version of C in your dependencies is up to how different 1.0 & 2.0 is, and how A & B use it. But if you want them resolved, it's up to you to do the engineering to A or B.