In this chapter, I'm going to make some seemingly disparate observations, and then at the end I'll tie them together. Please bear with me.
First of all, here is the area I'll be discussing as shown on Steve's Map:
The Southeast on Steve's Map
As you can see, the Duchy of Arylle's borders are shown on Steve's Map, but Luatha is just labeled (it's hard to read in the small image on the left, but Luatha is written about halfway up the Laughing River on the right).
However, Paarfi tells us that Arylle and Luatha share a border:
A quick aside: I think Paarfi misspoke when he wrote that "the southernmost [county], called Groomsman, extending to a point abutting the Duchy of Luatha"; I think he means that Groomsman is the northermost county.
When Sethra is explaining to Zerika et al how to get from Dzur Mountain to Deathgate Falls, she says that this border is also the transition point from jungle (to the south) to plains (to the north):
Paarfi says the political border is at "the edge of the Great Plains" and Sethra says Wilder is a location on "the edge of the Pushta", so that puts Wilder on the border between Arylle and Luatha. Since they will get to it after crossing the Laughing River, it's also to the northeast of the Laughing River:
Wilder's Location
When Morrolan et al make a similar trip in reverse (traveling from the East to the future home of Castle Black), they follow a road that appears to run in this same general area:
This suggests that there is a road that runs south between the Laughing River and the Shallow River all the way to Chorbis, and from there to Bellows, and from there to Nacine.
To remind you, here is how Paarfi/Sethra describes the road Zerika is to take on her journey northward:
I don't think that first road starts on Dzur Mountain itself; it probably runs either east or west of Dzur Mountain. As I've already established, there appears to be a road running north of Bra-moor to Undauntra's Highway; that road does not appear to go anywhere near the Laughing River, so I think the road Zerika took is to the east of Dzur Mountain, and that's also the location of the road Morrolan took.
While it's certainly possible that there are two roads that run north to the east of Dzur Mountain, a simpler explanation is that these are the same road.
That means this road runs from Nacine to Bellows to Chorbis to a good ford across the Laughing River, where it turns east. Just a little ways north of there, the road continues through Wilder to the north.
Southeastern Road
Rafts
Another potential stop along this road is Rafts (a village, a barony and a castle):
That straightline road from Chorbis to Wilder crosses the Laughing River exactly 100 miles north of where the Yendi River flows into the Laughing River.