The instant death/death check rules are not as legalistically clear as one might like, but the intent is that they count per attack. The grimlock's club is one attack even though it delivers multiple dice/types of damage, so the total is what is applied to the Instant Death rule. While the rule itself just says "damage remaining," where you might try to interpret that as "per die" or "per part of the damage," the example right below it says "if she takes 18 points of damage from an attack..." (emphasis mine). Therefore any damage from that attack - multiple types, energy stacked on, etc. - is all one big chunk of damage for purposes of these rules. Also see under "Damage,"

Each weapon, spell, and harmful monster ability specifies the damage it deals. You roll the damage die or dice, add any modifiers, and apply the damage to your target.

In your Scenario 1 that's simply 7 total points of damage from an attack and in Scenario 2 it's 9 total points of damage from an attack.

Yes.

The instant death/death check rules are not as legalistically clear as one might like, but the intent is that they count per attack. The grimlock's club is one attack even though it delivers multiple dice/types of damage, so the total is what is applied to the Instant Death rule.

See under "Damage,"

Each weapon, spell, and harmful monster ability specifies the damage it deals. You roll the damage die or dice, add any modifiers, and apply the damage to your target.

While the instant death rule itself just says "damage remaining," where you might try to interpret that as "per die" or "per part of the damage," the example right below it says "if she takes 18 points of damage from an attack..." (emphasis mine). Therefore any damage from that attack - multiple types, energy stacked on, etc. - is all one big chunk of damage for purposes of these rules.

In your Scenario 1 that's simply 7 total points of damage from an attack and in Scenario 2 it's 9 total points of damage from an attack.