Only issue here is those particular abilities do stack because they aren't divine bonuses. Axiomatic makes a weapon lawfully-aligned and infused with the power of law. Holy makes good-aligned and imbued with holy power. Sacred sheathes the weapon in positive energy. The stacking bonuses for these three actually vary depending on the target, but the +2 bonuses are only for purposes of costing the creation of a magic weapon.
Axiomatic weapons bypass DR and does an additional 2d6 damage to chaotic targets.
Holy weapons bypass DR and does an additional 2d6 damage to evil targets.
Sacred weapons are good aligned for purposes of bypassing DR, do 1d6 additional damage to undead, and 2d6 additional damage to outsiders.
Let's say a PC with a +3 Str bonus wields a weapon with these three abilities against a demon - say - a marilith. The marilith is a chaotic evil extraplanar outsider with DR 10/cold iron or good.
The PC gets a +3 Str bonus to attack and damage. The Axiomatic effect doesn't bypass the DR but does do 2d6 additional damage since the marilith is chaotic. The Holy and Sacred effects both can bypass DR and they both do an additional 2d6 damage since the marilith is both evil and an outsider. Result: + 3 attack bonus, +6d6+3 damage bonus, and no damage reduction.
Let's say it was against a vampire. Always evil, DR 10/silver and magic. +3 Str bonus. Axiomatic = no effect. Holy does 2d6 damage but does not bypass DR. Sacred does an additional 1d6 but does not bypass DR.
