So for many years I've had a certain belief about how vuln stacking works, but would like to just get it straight.

Example: fighting undead that is (for purposes of this discussion) vuln to silver and vuln to holy. I use a weapon that is made of silver, and has wrath attack. Am I getting 2x vuln damage? Do they stack or is the second vuln just wasted now?

Compare with a silver weapon that is not holy attack (and is something the undead is neither vuln nor resistant to, just regular). How much damage do I do in comparison?

Compare with a steel weapon that is holy? Same question.

How do the multipliers work?

Thanks!