(Few problems: a) It has to be one object, hence, 1 blade. b) for some reason, the object "should not be carried" - but let's assumed, they mean it is not attached, c) "The object flies in a straight line", meaning, Fran would have to move, otherwise, it will hit at least Lulu.

I strongly suspect, "a straight line" means straight line of empty squares. But if arrow can be shot at relatively close distance over someone, I guess Catapult can too, so, let's play it like this)

Devil's DEX save: 18

Squeaking runner managed to dodge the dagger, but Brutus got a chunk of devil's flesh out of M1.

Round 2

Ordrag

Ordrag will pummel the prone devil if it's still conscious, otherwise he'll turn any extra attacks at the one on the right.

Action: Attack/Longsword. Attack#1: 11 Damage: 8 (Adv roll: 10)
Attack#2: 14 Damage: 11 (Adv roll: 23)
Bonus Action: TWF/Warhammer. Attack: 15 Damage: 7 (Adv roll: 14)

No escape for you, bro. You die here, you die for real, Ordrag taunts.

It took all three attacks, but Ordrag finished the devil! Number one was done for. The body on the ground suddenly turned dirty grey, looking as a rock - and then silently crumbled into the pile of ashes.

Devil M3 watched the scene with a horror in his eyes, then turned and run after his fellow M2 (with the same success - suddenly difficult terrain did not let him get far).

Both remaining devils are running, both are at the border of the difficult terrain.

Choir, Polly.

Choir will run after the devils, trying to get close enough to cast Word of Radiance for 4 each. (Con save DC 16 )

(If she can't get that close, she will still run and just throw a javelin at M3 instead. Attack: 12 Damage: 7

Polly runs up to the corner of the house, raise her hand and yell “brisngr” and cast fire bolt on M1 only after realize her mistake that fiends resists fire damage. 

Attack: 24 Damage: 12 

(M1 is dead anyway, but M3 - yes, resisted the bolt) 14 3

Choir did manage to get close enough ((halves usually rounded down, but let's leave it up) - and party could enjoy the view of another devil crumbling to dust. (M2 is no more)

All what was left is a wounded M3, doing his best to escape terrible danger (in a shape of adventurers) behind.

Everyone can join the hunt now!

Adray will rush up to the last remaining demon and attempt to toss him to the ground.  If at first he doesn't succeed he will try again, if he does then he will attack him while he's down.

Trip check opposed by his athletics or acrobatics.  If he fails he is prone.  Check 1 19, check 2 if he resists the first 25

If he fails first trip attempt here is the follow up kick to the head. Attack: 27 Damage: 12

Side note: Adray's speed is 40 ft wi use Step of the wind for a ki point if unable to reach him normally.  That gives him 80 ft movement costing 1 ki point and his bonus action.

Adray, also struggling with unruly ground, managed to reach the devil and tried to push him down. (9, 10 ) The first attempt threw the creature to the ground, and Adray felt like his boot hit the thick skull. Devil - alive but terrified - was trying desperately to crawl away.  

Choir will also run after.

Kill or question? She doesn't have the time to conduct a discussion, so she whacks the devil with her Mace of Light, trying for non-lethal damage.

Attack: 12 Damage: 5

Ordrag also lays into the captured remaining devil. (I think Ordrag goes before Adray, therefore devil isn't prone yet, but in case I'm wrong, advantage rolls included)

Action: Attack/Longsword. Attack#1: 8 Damage: 7 (Adv roll: 9)
Attack#2: 24 Damage: 9 (Adv roll: 11)
Bonus Action: TWF/Warhammer. Attack: 7 Damage: 7 (Adv roll: 15)

(Damage for crit on attack #1 if advantage: Damage: 14)

Need Fran and Brutus here

(Sorry, I was waiting to see what all happened here. Got a little confused. Fran is pretty far away so...)

Fran will load her crossbow and take aim for the back of the devil's knees while Brutus navigates his way to their prey.

Attack: 7 Damage: 4

Bonus attack if Brutus can reach: 9 Damage: 7

To, probably, his own surprise, devil did not die still. He managed to crawl from under Adray's boot and Ordrag's weapon, and on all four run as fast as he could, happy to feel the solid again ground underneath.

M3 is 45ft away from Adray and Ordrag, 50ft from Choir.

Opportunity Attack?  Longsword: 9 Damage: 7

(I really don't mind if he gets away, mission still accomplished. If no OA, then Ordrag will look to see what became of the woman with children.)

Yep, he risked it and lost - even not silvered, the blade cut deep enough to kill the last devil (to Choir's disappointment. Though, she could realize fast enough, these were by far not the last devils the group was about to see).

The woman and two of her little boys seemed to be fine (children, fascinated by the little golden flying elephant already smiling, despite the danger they were in a moment ago). "We won!" declared Lulu, making another happy trumpet sound.

Adray winced at the horn, and turned around looking about. "Right, let's get off the main street for the moment, as useful as Lulu is, that trumpeting may alert others."

"We won!" Choir repeats. Probably safer to finish the thing off.  She doubts it would have made a very truthful tour guide.

Exhaling, relieved that fighting is over for now Polly walks over to Adrey. “For you who are natives of Elturel, is there anywhere we can hide and assess the situation and maybe come up with a plan?”

She then turn to the mother and child if they are still there. “Are you okey? Could you tell us a little about your situaton?”

"Your situation? But... you are here too, you had to know it as well!" The woman looked in surprise. "Oh, I'm sorry, I sound so ungrateful." She called back her children, that Lulu was entertaining and introduced the whole family: "My name is Harkina Hunt, these are my sons - Ezo and Brask" (twins smiled a bit shyly)"we were trying to find some food when those devils attacked. They swooped this street just two days ago, I did not expect them to come back so soon. Hoped to fined some food and then try to make it to the High Hal. Word is, west part of the city is less dangerous and there are some people keeping devils at bay".

"But where did you came from if you do not know these?"

Fran will look around warily. She was happy to be done with those devils, but she was with Polly on this one. What was the situation?  The artificer would call Brutus over to stay close with Lulu and the victims while she would go over to inspect the bodies of their dead foes.