Can green flame blade, slashing flourish, and sweeping maneuver be combined for a massive sweeping attack?

A character with the classes: Rogue(Arcane Trickster) lvl 3, Bard (College of Swords) lvl 4, Fighter (Battle Master) lvl 3, has:

  1. Green Flame blade.
  2. The Bardic College of Sword’s slashing flourish.
  3. Battle Master’s sweeping maneuver.

Can these be used in the same turn against the same 2 foes?

Character is fighting 2 opponents, Casts Green Flame blade and hits target and therefore the “jumping flame” portion of the spell hits the 2nd target as well, and since the attack hit the player decides to use both the flourish and sweep to deal even more damage to the second target.

Do both damage sources stack?

Can both be used at the same time?

Both the slashing flourish and the sweeping maneuver do not require an action nor bonus action to activate. For the attack, would both the flourish and maneuver apply should the player choose to use both resources?

Is it just down to a DM call?

Is there a creature that is resistant or immune to non-magical damage other than bludgeoning, slashing, and piercing?

Reading this question: Is there a distinction between magical damage and nonmagical damage?

I was wondering if there is a monster that is resistant or immune to non-magical damage other than the common bludgeoning, piercing, and slashing damage. For example, this monster might resist fire damage coming from a non-magical source, so using a torch might not be as effective as hurling a fire bolt at it.

Is there an example of such a creature?

Any damage resistance or immunity will do. If there is precedent or lore from an earlier edition that a creature has such a resistance/immunity, I would also welcome that information.

How can a Black Pudding split when damaged by lightning or slashing damage if it’s immune to such damage?

From DND Beyond entry on Black Pudding: (bold italics are mine)

Damage Immunities acid, cold, lightning, slashing

At the bottom of the stat block, under Reactions, it has the ability Split:

Split When a pudding that is Medium or larger is subjected to lightning or slashing damage, it splits into two new puddings if it has at least 10 hit points.

If it’s immune to lightning and slashing damage, how can it be ‘subjected’ to lightning or slashing damage in order to activate ‘Split’? It’s clear that ‘is subjected to’ means that it takes the damage. If you’re immune to something you by definition cannot be ‘subjected’ to it.