Zartan (100 feet away from Itzmin), Pax, and Bendrak (both 120 feet away) may act first.

(N.B. During a chase, a participant can freely use the Dash action a number of times equal to 3 + its Constitution modifier. Each additional Dash action it takes requires the creature to succeed on a DC 10 Constitution check at the end of its turn or gain 1 level of exhaustion.)

Pax sets off on a loping run. Seeing Itzmin headed towards the crowd, he calls out to Tuuli before she takes off in pursuit. He knows she is fast and will likely outrun them all. "Keep your eyes on him, Tuuli, he is slippery."

Zartan is looking to keep next to Tuuli. When close enough to her he asks, “capture or take out?”

Tulle's eyes widen at Pax's touch, and she nods. To Zartan as she races off, "I don't know!"

Zartan and Pax momentarily catch up with Tuuli. 
Bendrak and Tuuli are up next!

Tuuli chases Itzmin, trying to catch up, hopefully before he reaches the crowd.

Move: 30'
Action: Dash 30'
Cunning Action: Dash 30'

Total: 90'

Sprinting, Tuuli is able to catch up with Itzmin, and passes him, and with her back to the crowd ahead, tries to head him off at the end of the alley. The crowd behind her is loud and boisterous, but seemingly unalarmed by the commotion.

(Unless Bendrak has another action, we'll assume he Dashes 60' with the others.)

"Stay out of this!" commands Itzmin. He waves a bit of paper over himself and with an arcane word, a subtle shimmering field appears around his body.

(Note: "Chase participants can’t normally make opportunity attacks against each other, since they are all assumed to be moving in the same direction at the same time." But I'll allow one opportunity attack between Itzmin and Tuuli as they reach this bottleneck. )

Itzmin Dagger Opportunity Attack vs. Itzmin: 7. Hit: 5 piercing damage.

He then charges past, into the crowd. (Dash)

Tuuli may have an opportunity attack. Aranor and Walt may act next.

(No further opportunity attacks, unless conditions warrant.)

Watching his companions take off after Tuuli and Itzmin, Aranor shrugs and decides to follow, although he has no illusions he'll catch up with Itzmin in time. It will be up to Tuuli to deal with the duplicitous tiefling. He sets out at a moderate run.

Action: Dash 60'

Walt sighs and breaks out into a slow jog before kicking into high gear. Walt strains to keep sight on Itzmin and his friends. He see’s the tiefling attempt to slash Tuuli and Walt is infuriated. He dashes and then activates his ring of jumping to to help close the gap.

Move + dash + ring of jumping = 96ft of movement…I think?

Tuuli skips out of the way of Itzmin’s jab, raising her hands, “Hey! Woah! This is not that kind of chase, I just want to talk!”

Itzmin ignores Tuuli and barrels into the chaotic crowd.

Round Two:
Zartan, Pax, Bendrak, and Tuuli are up next!

"Son of a..." Tulli launches herself into the crowd after him. If she catches up to him, she will try to delay him by getting in his way, or grabbing him.

Move: 30'
Bonus Action: Cunning Action Dash 30' (or some smaller number that catches up to him)
Action: I guess this is a grapple? Which is the thing she's best at! (it's not.)

Athletics for grappling or bodying up Itzmin to slow him down (igl): 13

Pax keeps running (Dash 60').

(Oh goodness, I swear I'm still alive!)

Bendrak does indeed Dash, heart pounding as his sprint begins to slow.

In the middle of a chaotic crowd, full of food smells, kids, costumes, parades, and fireworks, Tuuli catches up to Itzmin and tries to grab him. Itzmin tries to dodge her. Acrobatics: 11

Meanwhile, Paz and Bendrak begin to catch up, and Zartan nears the end of the alley.

Itzmin is grappled. "Let go of me you lunatic! Help!"

Zartan, still in the alley, and 100 feet behind them, is up next.

Zartan dashes up to them

Sprinting, Zartan careens to the end of the alley and headlong into the crowded street.

Still shouting, Itzmin tries to squirm out of Tuuli's grasp. Itzmin-Acrobatics: 7 vs. Tuuli-Athletics: 7

The green-horned tiefling remains firmly in Tuuli's grip.

Aranor and Walt (and Lucky) may act next! (Tuuli and Itzmin have run around the corner, out of sight; only Zartan can everyone in the party.)

Tuuli continues to try to defuse the situation. “I’m not trying to hurt you! I just want to know what’s really going on with the owl demon!”

(Nothing like putting all her cards on the table! She’s not much for subterfuge.)