I get advantage because of the size difference right?

(Advantage on attacks? No.)

Worth a shot. Ill attack which ever drow i can see with my bite Attack: 14 Damage: 31 and swipe at were the other one might be with the tail Attack: 31 Damage: 27

If either are at disadvantage the rolls are bite 26 and tail 21

Eldin will try to look around for the other drow. Perception: 18

(SWEET!)

Eldin spots the drow and gives chase. He will stand next to the Drow (hopefully out of Darkness) and strike at him.

If Perception costs Bonus Action (Eye for Detail):
Rapier attack: 24 Dmg: 13

If Perception doesn't cost action:
Action: Grapple - Athletics: 27
Bonus Action: Spirit weapon: 20 (Adv:12) Dmg: 8
Movement: Move closer to G-Rex

For clarification: Eldin is targeting the drow that was trying to escape.

Grianne strikes at the Drow that wasn't able to move as the darkness falls, but he is able to avoid her strikes.

Eldin hears the drow fleeing and is able to keep up. He tries to grab him (Acrobatics: 9), as his spectral sword strikes. The drow parries the attack. He's trapped.

The first drow moves quietly into the darkness (Stealth: 23) He draws a small Crossbow and fires at Gryannosaurus, hitting 9 for 9 piercing. (Con save, and Concentration) the bolt is coated in a poison that doesn't cause her pain, but causes nausea.

The one chasing Eldin turns to face him again, stabbing 20 for 8 piercing, 11 poison, and 14 for 9 piercing, 5 poison. It's attacks are ineffective at best.

(Is it my turn again?)

Eldin will attack the Grappled drow again.

Rapier: 26 Dmg: 9
Spirit weapon: 15 Dmg: 8

Does the spirit weapon allow me to use Sneak Attack? If so: 15

Eldin stabs the Drow (Con: 6). His spectral sword swipes as well, but misses. The Darkness disappears and the first drow's silent movement dies little to conceal him...

(Yes, your turn. No spectral weapon doesn't count as an ally, but you get Sneak Attack from Insightful fighting)

(Grianne)

D1: 70 D2: 28 El: 26 Gr: 25

Eldin will tell Grianne, "Don't outright kill them. We need to figure out what they want."

Con save22  concentration check 22

Gryannosaurus will bite Attack: 23 Damage: 44 at the drow Eldin isnt trying to grapple and swings her tail Attack: 12 Damage: 21

She does her best to not kill the drow.

Grianne's target falls unconscious.

The remaining drow stabs at Eldin, trying to break free, hitting 18 for 7 piercing and 9 poison and 15 for 6 piercing and 11 poison.

(Eldin, Grianne)

D1: X D2: 28 El: 26 Gr: 25

Eldin moves the drow next to G-Rex so that the large dinosaur scares the drow enough for a clean hit.

Rapier Attack: 14 Dmg:10 + Sneak Attack: 7
Spirit Weapon: 8 Dmg: 6

The drow struggles against Eldin's incredible strengty, but he's able to avoid both attacks.

(Grianne)

G-Rex will gently place her foot on what ever part of the drow can be stepped on and wont kill him to lose if i dont like him very much and "Accidentally" crush him a little. 

I guess that's a grapple ? So a strength check is used?  12

(The one that's still conscious?)

If one of them still is, yes. 

Grianne helps to keep Eldin's target from escaping (Acrobatics: 23) pressing him into the mud.

The drow responds striking at her, hitting 22 for 7 piercing, 12 poison, and 16 for 9 piercing, 7 poison. G-Rex can do little to avoid the little mosquito bites. (Concentration ×2)

"I hadn't intended to kill anyone tonight, but if I must I will." He spits.

(Eldin, Grianne)

D1: X D2: 28 El: 26 Gr: 60

Concentration checks 1 21 and 2 20

I break his legs.

And roar loudly in his face

Make an attack roll without damage to break his legs.

Breaking Legs roll 20

He cries out in pain, but withstands the force of your stomp, which presses his legs down into the soft mud.

(Eldin)