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

Question

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?

Answer 1

No

Green Flame Blade is a cantrip: casting it requires the Cast a Spell action.

Slashing Flourish requires you to take the Attack action - this is not the Cast a Spell action so they cannot be combined.

Sweeping Maneuver only requires an attack - this is compatible with either Green Flame Blade or Slashing Flourish but not both because they are not compatible with each other.

Answer 2

It doesn't quite work.

First, the Battle Master's Sweeping Attack (PHB p74) ability seems to work fine as it says:

When you hit a creature with a melee weapon attack...

And Green Flameblade says (SCAG p143):

As part of the action used to cast this spell, you must make a melee attack with a weapon

The issue comes when you consider the action used. In this case you are using the Cast a Spell action not an Attack action and those are very different for the purposes of this system. PHB 192 has that information on the differences.

For your Bard's Slashing Flourish (XGtE p15 emphasis mine):

Whenever you take the Attack action on your turn

Therefore at least this part of the plan will not work.