Charge penalties

When you charge, you automatically switch to your hands. Does this cede advantage, or do you retain it just long enough to resolve the charge and see which way things go?

In the Mazarbul fight in the arena, the cave troll won advantage (Mattock/longest), but then charged. Does he have to pay a +3 Ob penalty for acting with his (Short) hands? That would make a world of difference.

Change Weapons and you loose advantage immediately.

Yup. The advantage shifts to your opponent before the Charge is resolved.