(looking through the game log, there have been 3 persuasion rolls. And taking into account the advantage is a 15 which passes. I'm out today but when I get chance I'll update this post with the horses response) 

Maxeene replies "I recall giving a ride to a sun elf and his half-orc bodyguard two days ago; I picked them up at an intersection and dropped them off at the Yawning Portal. They talked about hiring spies to root out Xanathar Guild hideouts in the city." Maxeene’s descriptions of the passengers match the appearances of Davil Starsong and Yagra Stonefist.

Skye sweats as Maxeene speaks, but breathes more easily as she avoids mention.

”Did they talk about where they were hiring, or from where? What are they planning with regards to Xanathar’s guild? What more can you tell us?” 

"That is all they mentioned when I was giving them a lift."

Damros listens and puts all Maxeene says to memory.   "Thank you.  All you noted is appreciated.  I will alert Mirt of your cooperation.   Unless you have anything more to share, I shall bid you a good day."     

He looks to Skye to see if she has anything to ask or add.

Skye thinks for a minute, then sniffs. “Thanks.” And she turns away with Damros to report back. 

Sehaethas says in Kylaski's voice, "Goodbye Maxeene!"

Sehaethas shakes his head and then says in his own voice, "So now we all go and report?"

The question is, do you report to the Zhents or the Harpers first?

Xaul, who didn't feel it necassary to interact with Maxeene, hung back nearby as the party spoke to her, sticking around in case the lead ended up being a set up or the like. Luckily, it didn't come to that, and the party managed to get the question they need very easily, in fact. In response to Sehaethas' question, he says 'We could report to the Zhents first so we're concluding tasks in the order we completed them, however it might be easier and safer to inform the Harpers first. I don't mind either way.'

“Bleed the Zhents, take their gold. Then inform the Harpers. I like cake, and I like to eat.”

Damros nods at Skye's assessment.   Gold in hand; then distribute the information 'freely'.

You head to the Yawning Portal where you meet with Davil, Yagra sat next to him. He gets you a drink (if you wish) and then waits to hear how it went.

Damros recounts their search to even find Maxeene let alone be in a spot to speak with the horse.  He will deliver the little they gained from the encounter.  

"... and then Maxeene said she remembered giving a ride to a sun elf and his half-orc bodyguard two days ago.   And how she dropped them off at the Yawning Portal as they talked about hiring spies to root out Xanathar Guild hideouts in the city."

Damros scratches his chin while in deep thought.  "It doesn't seem to me like much to go on."

Skye puts a tankard down too heavily. She nods. “—what he said.” As Damros speaks she glowers at the Zhent. 

Davil doesn't look surprised at all. "I am glad that Maxeene was paying attention. We had to wait a while to make sure we were with the right horse. The Harpers already know of me and Yagra so we wanted to let them know that we are on their side and wish to remove the threat of the gang warfare as much as they do. And what of your mission for us? Have you found anything out about the murders in the dock ward?"

Xaul steps forward, giving a nod of recognition to his fellow half-orc friend Yagra, and says 'He's been dealt with. The body's currently at the bottom of the Dock Ward blue, but we've got a few of his belongings to prove that he's been killed off.' He dumps the pistol and a few of the other items onto the table, and says 'The killings should now cease seeing as he's dead, so if these items don't suffice, hopefully that should be proof enough that this problem has been dealt with effectively.'

Unlike when mentioning the information about him from Maxeene, he does look surprised at this, pleasantly surprised though. "I am impressed. I was expecting you to do some recon and intel gathering, and we would have dispatched our master assassin but that seems unnecessary now. Well I suppose a larger payment is in order." and after moving a few coins between pouches, he places a bag of 10 Harbour Moons onto the table (each Harbour Moon is equivalent in value to 50 dragons)

Damros tries to not react upon seeing the heavy bag of Harbour Moons dropped onto the table. 

Nervously, he will clear his throat and look between Xaul and Davil,  "We are good then?  Is there more to all this? Have we painted a target on our backs?" 

He sweeps an arm around the table, "Are we square or is there more to what went on out at the dock that we should know about - or at least be aware of in case we have assassins waiting in every shadow?"

Xaul has a similar reaction to Damros, barely managing to contain his shock at the reward presented. He's never seen an amount of money even close to that pile in his life. It'll certainly be a big helping hand towards tavern restoration. He clears his throat as Damros finishes speaking and adds 'Mind you, if there are any caveats that come along as a result of this quest,  I can speak confidently when I say that as a party we're all more than prepared to face them ourselves with same might we put into this job, especially seeing how generous you have been with our reward; it is much appreciated.' He flashes a grin at the Zhent, hoping he's said enough to compensate for Damros' questions. It was wise of the shadow elf to pry further on what matters might lie ahead because of the party's actions ( if he had came alone, Xaul probably would have just taken the money without a single thought for the consequences of the acts done to acquire it), but he also wants to make sure that the party holds onto their presented strength; as a performer and half-orc, he knows that looking and acting tough can sometimes be all a person needs to be percieved as strong.

Skye is of a like mind. “We’re square then. Winged Snake knows where to find us if you’ve got work to do and too many dragons weighing you down.” She drains the rest of her tankard in one pull and sets it down on the table as she stands. “Thanks.”

She jerks her head at the others and turns to leave.