Melwan, Fearil, Dearg, and Loch Varn are very close to each other because they gather for joint celebrations (Book 3, p.98 - Gaol: Of Love and Fury resurgence). Dearg acts as the central point between the other three. Melwan is past Neart's Stronghold (map on p.17 of Book 3), and southwest of Dearg.
To answer your other question, Dohag's Pass (used in the Loch Varn scenario) is shown on a mini-map on page 39 of Book 0 - Prologue. It looks like it is south of the Vale of Melwan, but I think it is rotated because Loch Varn is almost directly East in relation to Dearg. I think the pass is between them as you exit the Vale of Dearg. You can clearly see an Inguard on the mountain-tops in Book 3 that kinda matches the one in the Prologue book diagram.
I'm assuming true North based on the pennisula and continent map, not the zoomed-in versions in the books. A compass might have been nice.
As for the Distances...
According to the
Map Tool, Dearg and Melwan are exactly 23.368 km (14.5 miles) apart on their own road (not the one linking Melwan to Loch Varn). Assuming a normal walking pace on Flat terrain (3 mph), it will take 6 hours. I think the Map Tool always uses Forest terrain for some reason (2.5mph) so its more like 5 hours, which makes more sense since according to the map the roads runs along a mountain through woods.
Book 2 - Travels has the walking speeds on page 50.
Alternatively, I printed a map and used a ruler to make a inch-to-mile scale and made my own set of "makeshift values" and they came damn close to the official ones.
My value for Dearg is 18 miles and makes for longer trips than the official distances. I rate the difficulty as being Forest terrain (2.5mph on Foot) which should take 7 hours instead when using my value.
However, it all depends on the Travel skill of the players and how many hours they can walk in a day.
Travel 0: 2 hours/day
Travel 1-3: 5 hours/day
Travel 4-5: 10 hours/day
BUT BUT BUT keep in mind that the Map Tool uses 8 hours to calculate its "day" total. So 1 day, 2 hours is actually 8 hr + 2hr = 10 hours, which an expert Varigal can do in a single day without having to rest for a night.
Hope that helps!