My question is mainly concerning Eidolons and damage stacking abilities.
An eidolon has an evolution called Improved damage that states it increases the die rolls for a specific attack by one step.
One of the eidolon’s natural attacks is particularly deadly. Select one natural attack form and increase the damage die type by one step.
Along with that there is a feat of a similar name called Improved natural damage that does the same thing, of increasing damage by one step.
Choose one of the creature's natural attack forms (not an unarmed strike). The damage for this natural attack increases by one step on the following list, as if the creature's size had increased by one category. Damage dice increase as follows: 1d2, 1d3, 1d4, 1d6, 1d8, 2d6, 3d6, 4d6, 6d6, 8d6, 12d6.
Lastly an amulet of mighty fists can get the +2 enchantment of impact which also does a similar effect.
This special ability can only be placed on melee weapons that are not light weapons. An impact weapon delivers a potent kinetic jolt when it strikes, dealing damage as if the weapon were one size category larger.
Legally would all these stack? And if so would they also stack with the eidolon evolutions of making the creature large/Huge and/or using enlarge person on it?