In such cases, use the Wounds characteristic of the crew.

A cannon does not require a line of sight to the strike point. However, if anything that would stop a cannonball from bouncing (see 5. Crunch, on page 227) lies between the target point and the strike point, the cannonball will hit it and stop. In other words, you cannot use a high result on the Artillery dice to 'glitch' a cannonball through an impregnable obstacle.

No, a cannon cannot shoot over such obstacles, even if it is on a hill. However, a stone thrower can if it chooses to fire indirectly.

Not unless that cannon is on a hill and the unit is not. However, as above, a stone thrower can if it chooses to fire indirectly.

No. Page 143 of the rulebook makes it clear that, except in rare cases, units cannot shoot enemy units that are engaged in combat. In the case of cannon, this means the target point cannot be placed in such a way as to risk the cannonball hitting a friendly unit, or an enemy unit engaged in combat with a friendly unit.

Only cannons or weapons that fire using the 'Cannon Fire' special rule may also fire 'Grapeshot', as described on page 227 of the Warhammer: The Old World rulebook. This is in addition to any other special rules or additional modes of fire the weapon may have.

No. Because a war machine and its crew are treated as a single model, you must use the crew's BS.

Yes.