The source of the Hightower Brook is almost certainly north of Nacine and somewhere in the Collier Hills; I guessed it starts near Dzur Mountain and drew it flowing from there to Nacine, and then south to the coast.
Lostoar Brook
Paarfi says it runs 40-45 miles south of Dzur Mountain, but then goes on to say that it had crept into the county to the south of Southmoor (Iadim). Steve's Map shows the southern border of Southmoor, and it's further than 45 miles from the center of Dzur Mountain, so I guessed this direction was from the southern slopes (that is, 25-30 miles from the peak, plus 40-45 more miles, or about 65 miles south of the peak).
Since it runs east to west, it almost certainly runs into the Hightower Brook. I guessed it started in the hilly region to the east of Dzur Mountain.
Six Horses
I put Six Horses 25-30 miles north of the peak of South Mountain, then marked Tsira's house 1.5 miles west and 6 miles south of that point.
Knuckle Mountains
I might be making too much of the name, but I guessed that the Knuckle Mountains (especially in relation to an area called the Fingers) resembled the knuckles of a human hand. I guessed they extend across all three fingers, but to make them more "knuckle like", I drew them with north/south valleys.