BlackOllie wrote:1) During overwatch can a unit 'snap-shot' grenades? If they can are they limited to 1 per unit (like the shooting phase) or can every model equipped with them in a unit throw them (because this is not the shooting phase)? Does this change if the unit threw a grenade in the shooting phase?
Yes you can overwatch with them.
The 1 shot limit is on shooting attacks, not the shooting phase, and this is very much a shooting attack.
2) During the fight sub-phase can every model in a unit throw a grenade (again because this is not the shooting phase), or can only one model per unit throw them (like the shooting phase rules)? Does this change if a unit threw a grenade in the shooting phase?
Do you mean make a close combat attack with them? In which case yes every model can make a single attack with them.
3) If grenades can be thrown in overwatch can they be used again in the fight sub-phase for a total of 2 instances where grenades are thrown in the assault phase?
Yes, there's no limit on their use.