Resolving this:

Firstly Gimmond, you can make it with full movement. It's wis save 18 so passes goading attack, but is sapped. Str save 9 so it falls taking an additional 5 damage. 

Zumfir, a nat 20 cha save (for 22 total) means it's not banished. But it did get a 7 against grovel. (does nothing until it's turn) 

Twinkle, it fails the save on the first attack, which doesn't make it prone as movement isn't affected, but does grant advantage (not that any is needed). All attacks hit. 

On their turn, the stunned one grovels, falling prone, taking 5 damage (coincidentally the same. I rolled fall damage publicly in the game log as you guys technically inflicted it) and ending their turn (but couldn't do any other action anyway due to stun)

The other gets up and attacks Gimmond from above so back at 10ft up. (first attack at disadvantage from sap).

It attempts to ram you with its ram head with an 11 to hit.Then the lion head tries to bite, 26 to hit for 9 piercing damage. Finally the dragon head breathes fire. Due to everyone else being by the other chimera, and it being angry and not smart, it only reaches Gimmond. Dex save 15, 44 fire damage on a failure, half on success.

Everyone is up, all attacks (except Twinkle) on the prone one have advantage and it auto fails dex and str saves due to stun. For Twinkle, she needs to be in melee for advantage from prone as stunned ends. 

Athos will draw his dragon's wrath longsword and move up to the prone chimera to take two swings with advantage.  He gets a 14 (13,14) to hit for the first attack for 10 slashing and 12 fire damage.  His second attack gets a 13 to hit (13,11) for 9 slashing and 3 fire damage.

( cries in enemy nat 20 )

Cursing under his breath, Zumfir will raise Niko's mace to summon a celestial next to the fallen chimera, turning it into a DEFENDER. "Attack them!" He ordered, and the defender complied.

Attack: 19 Damage: 10 Attack: 19 Damage: 12

Then, it points its radiant mace towards Athos, giving him 8 temporary hitpoints, as well as giving itself 10 THP

After being caught off guard by the horns Gimmond takes the blast almost full on and nearly left a smoldering mess by the time the flames die down. But after coughing up both smoke and blood, the very much heavily injured dwarf not only held his position, but ascended further to try and drive his chimera back down into the ground. His first few strokes is either parried by goat horns or hindered by his injuries. Yet with renewed vigor(action surge), he double downs with such ferocity that the beast may surely be driven back earthward if it yields even the slightest bit to the assault.

Mo: Fly up 5ft above Chimera(#1).
Ba: Second Wind, regaining 13 Hp.

Ac: Attack Chimera(#1) with a most vicious spear!
Attack #1:  One-Handed Vicious Spear vs Chimera #1(AC ??) - To Hit: 9 For: - Piercing Damage. 
Attack #2:  One-Handed Vicious Spear vs Chimera #1(AC ??) - To Hit: 10 For: - Piercing Damage. 
Action Surge
Attack #3:  One-Handed Vicious Spear vs Chimera #1(AC ??) - To Hit: 21 For: 17 Piercing Damage. (Weapon damaged rolled twice w/ Savage Attacker)
Attack #4:  One-Handed Vicious Spear vs Chimera #1(AC ??) - To Hit: 27(Nat 20) For: 33 Piercing Damage. 
On second hit, using Trip Attack Again. STR Save(DC 15) or fall prone again, taking fall damage.
Also sapping target, causing 1st attack from it to be at disadvantage.

Note: Bonus damage from maneuvers included in overall damage.

Twinkle grins and rushes at the chimera that was commanded to grovel by Athos. The monk exploits the fact that it's prone, moving within 5 feet and unleashing a barrage of punches. Not wanting to let it get away, she tries to stun it a second time.

Action:
Attack 1: 16/25 damage: 11 force + Stunning Strike (Con Save DC 14: Failure: Stunned until start of Twinkles next turn, Success: chimeras speed is halved until the start of Twinkles next turn and next attack against it before then has advantage.)
Attack 2: 22/26, damage: 14 force

Bonus Action [Flurry of Blows]:  
Attack 3: 15/20, damage: 9 force
Attack 4: 13/21, damage: 14 force

Athos hits with his first, but narrowly misses with his second strike.

The radiant defender gets two solid strikes in. 

And then Twinkle hits with all attacks. Stunning strike doesn't trigger, because death overrides it. (in fact, the final flurry of blows attack was not needed. It was dead in 3 attacks, but I belive you have to spend the ki before rolling?)

Gimmond has singlehandedly got his one bloodied. But it's not tripped this time. It retaliates in force. The ram head (disadvantage) misses (11), the lion head (26) bites, for 12 piercing, and the dragon head (fire breath doesn't recharge) barely hits (23) with its claw for 8 slashing damage. (20 total damage.)

Everyone is up 

Gimmond puts on a good show deflecting the ram head, but it's clear his wounds were beginning to take its toll as the other heads rip into him. Only share dwarven grit and stubbornness allows him to power through and eventually free himself from the deadly maw, though his armor was red more from his own blood than the creature at this point.

Exhausted as he was, Gimmond took a moment to steady himself for what might be the last time this match, before throwing himself at the beast with more reckless abandon, catching the goat head first across the eye with the first stroke, before zipping around driving his spear down upon its center mass with his full weight behind the follow-up. "Fall, damnable beast, fall!" 

Ba: Second Wind, regaining 15 Hp.

Ac: Attack Chimera(#1) with a most vicious spear!
Attack #1:  One-Handed Vicious Spear vs Chimera #1(AC ??) - To Hit: 22 For: 13 Piercing Damage. 
Attack #2:  One-Handed Vicious Spear vs Chimera #1(AC ??) - To Hit: 19 For: 22 Piercing Damage. 
If hit, tripping one final time on that last attack. Strength Save(DC 15) or be knocked prone.

Str save: 14. So it falls taking 1d6 bludgeoning (4). It looks extremely injured. It's now on 2hp so someome should finish it off 

[Yeah, I have to spend the ki / focus points to activate flurry before taking the bonus action. All good through!]

Twinkle rushes up and rams the chimera from the side with a double leg kick right in the head. 

Action:
Attack 1: 16 damage: 13 force
Attack 2: 12

In case 16 doesn't hit, bonus action single punch: 19 to hit for 9 damage.

You can tell it hits as Athos hit with a 14 but missed with a 13 (giving the AC quite nicely). Twinkle got the killing blow on both beasts, showing how much of a powerhouse she is.

You level up again, and this time get 1000gp.