Chapter One: The Iron Sphere of Sthombo

I assume it's our round again, and the final guy lost his turn due to being knocked over?

The second assailant crumpled to the ground, blood spewing from his neck Felow turns his attention to the remaining, unseen foe in the bushes. He mutters a cantrip under his breath, and begins to speak with an unnaturally deep, thundering voice:
"YOU THERE, IN THE THICKETS! YOUR PLAN HAS FAILED AND YOUR ARE SURROUNDED! IN THE NAME OF THE MOUNTAIN GOD, SURRENDER NOW AND WE WILL SPARE YOUR PITIFUL LIFE!"

Cast Thaumaturgy (captrip), with the effect: Your voice booms up to three times as loud as normal for 1 minute
I'm trying to intimidate the guy into surrendering, not sure if I need some kind of roll/skill check to go along with the spell?

Cursing some more as his second bolt fails to find its target Vad stows his crossbow and runs up to where Felor is yelling at the injured ambushers. Hearing no response Vad shrugs his shoulders and raises his right hand, palm up, into the air. Producing a red glowing ball about two feet in diameter directly above his hand he turns to Felor and says, as loudly as possible, "I guess they've chosen death."

Prestidigitation cantrip to produce the glowing ball. Vad is also trying to intimidate and figures his obvious magic may come across as a little more threatening than a booming voice.

Leth lowered his bow, though an arrow was still set on the string should he need it. He said just loud enough that those around him - and hopefully not the three mystery figures in the bushes - could hear him: "Well... at least they're not attacking us anymore. Perhaps they're dead or otherwise incapacitated... We should check. See if we can keep one of them alive. I want to get to the bottom of this."

Tzipporah steps forward to the bush with last attacker still hiding in it. As she pushed aside the branches she puts on a honeyed and soothing voice, " My companions will slay you if you do not surrender. I don't want that, you don't want that. Whoever paid you do make this attack, it was not worth your life. Live to fight another day. I will ensure it."

Vad will walk over to the two dead ambushers and retrieve one of his crossbow bolts.

Shield still held up and spear at the ready, Felor gingerly inches around the thicket. When the prone form of the third ambusher comes into view, he approaches slowly and holds the tip of his spear to the attacker's neck.
"You still alive?"

Not quite clear on the mechanics of NPC death, but if this guy is at the "alive but will die if not stabilised" state, I will use Spare The Dying (cantrip) to stabilise the guy. I then have rope that someone can use to tie him up (or I can do that if we're not limited to 1 action per turn now).

Felor slings his shield around onto his back, and then works quickly to stabilise the injured man, muttering a short invocation to the gods and placing some absorbent moss over a gash on his forehead to stop the bleeding. Taking a length of rope from his pack, he binds the man's hands and ankles securely, and steps away, happy to let a more eloquent and persuasive party member take over the questioning when the man awakes.

Minus 8 feet of rope.

Tzipporah kneals down next to the bound foe, brushing her hair back from her face. She looks him over trying to get a read on the man. "Who sent him and from where" she wondered to herself. Reaching out she gently caressed the man's cheek. And then she sharply strikes his across the face. "Wake assassin. You have answers to give."

Vad walks over to Tzipporah and whispers to her so that the prisoner won't hear, "I wonder if he knows anything about where Zora may have run off to. If he's hurt her..."

"Trust me, my bound friend, you are gonna wanna tell us everything you know. I can't protect you from the others unless you give them something." Tzipporah's voice was soothing and silky.