What is the order of resolving crits?

I I have to draw 3 crit cards

Scenario A:

Draw first card, read text and resolve (for example to draw another crits etc)

Then, after resolving everything, draw the second crit etc

Scenario B:

Draw all 3 cards at once, the begin to read and resolve the first one etc

Damage cards are drawn one at a time. So I'd say you'd resolve each crit as you draw it.

Also the rules say "that card is dealt faceup and its text immediately resolves."

Yup.

It matters in particular with Major Explosion.

VanorDM is correct, you draw one and resolve it before drawing another.

You should not know what the next crit is as you resolve the current one. Most cards don't give you any decisions to make, so knowing what comes next is moot, but some do and it could, technically, affect your decision.

Example : Which secondary weapon you discard from Munitions Failure could be affected by knowing what the next crits are.

Possibly a more common example: whether or not you pop the Integrated Astromech on the first critical would most definitely be affected by knowing what's up next.

One at a time. So you resolve that crit before you draw the next, including any "Discard that card" effects ala Chewy crew or IA. Once you draw the next card, you opt out of those options on the last one.