You have two solid steel spheres; sphere 2 has twice the radius of sphere 1. what is the ratio of the moments of inertia, i2 : i1?

You made an assumption that was incorrect. You assumed that the masses were the same. However, since they were both steel then the larger one would have a mass of 2^3 or eight times the smaller (v is proportional to r^3). So the larger one would have an I 8*4 or 32 times the smaller one.