For the first question, the Holy Strike does not stack with Holy Weapon, but I assume it does stack with Sacred Weapon, am I correct?Secondly, Holy Strike gives a 1d6 bonus. Does this double to a 2d6 with a confirmed critical hit? I think so, just checking.
1. Yes, it stacks with Sacred Weapon, EXCEPT that if you use Sacred Weapon to give your weapon the Holy enchantment, Holy Strike won't stack with the Holy enchantment (you use the better of the two).
2. The ability description doesn't specifically state one way or the other, so the general rule applies. As stated in the PRD under Multiplying Damage: "Extra damage dice over and above a weapon's normal damage are never multiplied."