A 105 a Leadership requires you to explicitly work with your DM to determine what are appropriate cohort and followers. A DM could absolutely allow you to use Corpse/Bone creatures as followers of the appropriate modified level (though not as a cohort, since cohorts must have published level adjustments by RAW).

A 105 b No, Half-Golem cannot be applied to undead.

A 105 c A Half-Golem Corpse creature cannot exist, and thus cannot be a follower, or be controlled.

A 106 Yes, as long as you're the one casting it.