I seem to be related to Rev William Guthrie through one of his daughters, Agnes Guthrie, through the Millar line. I have accumulated the following information:
Burke's Peerage, Baronetage & Knightage, 107th edition has:
"Matthew Miller esq of Glenlee in the stuartry of Kircudbright m. Agnes daughter of the Rev William Guthrie Minister of Fenwick and was s by his eldest son, John Miller esq of Glenlee who m. Grizel...Cathcart"
Agnes Millar nee Guthrie died Aft 1697 at Glasgow, Lanarkshire, and Matthew Millar died abt Jan 1702 at Glenlee, Kirkcudbrightshire.
From the preface to his book "The Christian's Great Interest", Rev William Guthrie was born the eldest son of the laird of Pitforthly in Angus. He was also apparently a "cousin" of the Rev James Guthrie, the Martyr. Whilst preaching at Galston he was called to Fenwick. He helped decide where the church should be erected, preached a within its unfinished walls and was ordained 7 Nov 1644.
In August 1644 or 1645 he married Agnes Campbell, a distant relative of the Earl of Loudon, "of the noble family of Loudon", daughter of David Campbell of Skeldon House in the parish of Dalrymple, Ayrshire.
After 8 to 10 days' illness he died in the house of his brother-in-law Mr Lewis Skinner, minister at Brechin, upon Wednesday the 10th of Oct 1665, afternoon, in the 45th years of his age, and was buried in the church of Brechin, under Pitforthy's desk.
However his father's name is as yet a mystery to me. Some seem to connect him to John Guthrie (est 1577-1649) m. c.1599 to Nichola(s) Wood (est 1577–1645). If so his mother seems quite old for a birth in 1620.
So I'd be interested where you located his fathers name as James, and his mothers name as Janet.
According to the preface to his book, William Guthrie was born in 1620 son of the laird in Pitforthy, near Brechin, Forfarshire. I note from The Dictionary of National Biography and also
http://www.covenanter.org.uk/WilliamGuthrie/ that his mother was of the house of Easter Ogle, parish of Tannadice, Forfarshire.
"William remained in Fenwick for a few months longer before ill health and the death of the brother, to whom he had foregone his inheritance, took him back to Pitforthy. There he died on the 10th October 1665 aged 45" [http://en.wikisource.org/wiki/Guthrie,_William_%281620-1665%29_%28DNB00%29], at the home of his brother-in-law at Brechin, Angus. [Preface to The Christian’s Great Interest 1668]
"He was interred in Brechin cathedral. In 1854 a memorial to Guthrie was erected in Fenwick churchyard. In 2005 a plaque was erected in Brechin Cathedral to Guthrie by the Scottish Covenanter Memorials Association."[http://www.covenanter.org.uk/WilliamGuthrie/].
The monument says:
"In Memory of The Rev William Guthrie First Minister of this Parish and author of the Christians Great Interest Born 1620 Ordained 1644 Ejected by prelatic persecution 1664 Worn out by labours and sufferings he died 1665 and was interred in the church of Brechen His active and self-denied ministry through the divine blessing produced a deep and lasting impression. This stone is erected 1854 as a token of gratitude by the Christian Public"
"Two daughters of a family of six children survived him, one of whom became the wife of the Rev. Patrick Warner, of Irvine, and mother of Margaret Warner, who was afterwards married to the Rev. Robert Wodrow, of Eastwood, the faithful chronicler of the sufferings of the Church of Scotland."[http://www.covenanter.org.uk/WilliamGuthrie/]
I have his daughters as Agnes Guthrie (1656 – 1697) and Mary Guthrie (1665 – )
What were the names of his two sons that predeceased him?