Multiple damage types - Damage Calculations (Sulphur Haze)

[johanafm]

Sulphur Haze damage is listed as
Fire, Poison, Magic: 1

I know Magic is not a damage type that is applied, but rather affects resists and immunities.

A. How much damage is done?
That leaves Fire and Poison. Does that mean this spell does
1 Fire + 1 poison = 2 damage?
1 damage split over both: 0.5 Fire, 0.5 Poison (rounded to what)

B. How is damage resisted?
1 damage, but with double the chance to resist it (one attempt to resist poison, one attempt to resist fire)
1 damage, but requiring to resist both fire and poison to take no damage?
And is resistance flat subtraction of (input damage - resistance = damage taken), or is it chance based (each point of resistance gives some chance to resist some amount of damage).

B. Are there other spells with multiple damage types?

C. Do the same calculations apply to lingering?