It appears that his father Jonathan didn’t leave a will, at least that was recorded in the York Probate Records, however maybe you would be able to find some other probate document establishing the relationship of Jonathan b. 1650 and Jonathan b. 1680. This site of Deeds and Court records may be worth a look?
http://www.mainegenealogy.net/maine_wills.asp?source=probatecourtvol6&testator=JonathanNason
You have probably already seen this source of lineage.
Historic Homes and Places and Genealogical and Personal Memoirs Relating to the Families of Middlesex County, Massachusetts , Volume 1 William Richard Cutter
http://books.google.com/books?id=XowsAAAAYAAJ&pg=PA360&lpg=PA360&dq=jonathan+nason:sarah+jenkins&source=bl&ots=xnCtaEaEL7&sig=7Mh5hydQFmTPIvjSFkm7tLJgojI&hl=en&sa=X&ei=-d9qUI3nK4Ty0gHWmoDQBQ&ved=0CC4Q6AEwAw#v=onepage&q=jonathan%20nason%3Asarah%20jenkins&f=false
Jonathan Nason, son of Richard Nason 1, was born about 1650. Married Sarah Jenkins daughter of Reynolds Jenkins. He had a grant of land of a hundred acres in 1670, was constable in 1682, was killed probably by accident in 1691. His widow Sarah married John Kay Sr. of Berwick.
Children of Jonathan and Sarah Nason
1 Mary born about 1675 married October 6 1693 James Grant .
2 Sarah married Henry Snow.
3 Jonathan mentioned below.
4 Alice married Joseph Abbot
5 Abigail married January 3 1694 John Abbot
6 Charity married April 6 1696 Job Emery.
Jonathan Nason 2 was born about 1680 in Kittery Maine. He married April 27, 1702 Adah Morrell daughter of John and Sarah (Hodsden) Morrell. Both were baptized and owned the convenant at Berwick April 13, 1712. His will dated November 4, 1745 was probated April 7, 1746. His wife Adah survived him. Children:
1 Richard born February 14 1703 mentioned below.
2 John born October 24 1704 married Margaret Lord.
3 Mary born November 30 1706 married September 3, 1730 Matthew Libby.
4 Sarah born November 25 1708 married James Frost Jr of Berwick December 25 1729.
5 Jonathan born November 7 1710
6 Uriah born January 31 1712 13 married Sarah Stone of Wells and had a son Jeremiah born September 23 1741.
7 Adah born January 6 1714 15 married December 3 1747 Benjamin Wormwood of Wells.
8 Azariah born July 25 1716 married Abigail Staples.
9 Philadelphia born December 28 1719 married January 12 1742 James Rankin of Wells; second August 12 1756 John Harvey, she died aged one hundred and two years.
10 Rachel born May 1 1724
11 Elizabeth born May 27 1727 married February 7 1750 James Goold