1. Spoiler-type questions should be posted in the appropriate forum. In this case, Pyramid of the Sky Pharaoh (GM Reference).
2. Hakotep can only have 1 shield other active on him. The other 3 shield guardians have their shield other castings available to use in the event the active one on Hakotep is dispelled.
3. All damage, regardless of whether it's from a critical hit, is halved. 50% on the target (Hakotep), and 50% caster (shield guardian). If an odd amount of damage is dealt, the extra point is taken by the target. For example, 101 points of damage is dealt, target would take 51 points and caster would take 50.
Hope that helps!