Hi Janet,
I've just come across your post. I believe William is my 5 x great grandfather and possibly born around 1737. At Durham Records Online you can do a free basic search and you should find that William was married twice prior to his marriage to Phillis. I have included my notes below;
Widower and Husbandman (farmer) when married to Phillis Murton in 1781. Marriage Bond 11/3/1781, also signed by Francis Collingwood (glazier) of Ford, Northumberland.
Married twice previously in 1770 and 1775. Address on each occasion was either Tuggal or Tughill Hall, Bamburgh, Northumberland in the Durham Diocese.
William's age is given as 30 in 1770, 38 in 1775 and 21 years and upwards in 1781.
First two marriages;
7/6/1770 - Ann Smailes of Swinhoe, Barmbrough.
Marriage bond 20/5/1770, also signed by George Smailes of Berwick upon Tweed, Durham. William is a batchelor aged 30. The marriage took place at the groom's parish church.
(William's surname spelt Middlemas on Find My Past)
6/6/1775 - Margaret Blackbrough/Blackburg, age 28, spinster, at St. Maurice's church, Ellingham
Bride's parish - parish of Ellingham, South Charlton, Northumberland.
Groom's parish - Tuggal
Marriage bond 30/4/1775 co-signed by William Murdie of Chillingham, Northumberland. William Middlemass is a widower.
Possibly buried on 16/8/1796 at St. Ebba Beadnell (Beadnell parish register) but I can't confirm this.
I hope this helps with your research. The above dates make the 1736 baptism mentioned by Brentor boy a real possibility, as does the Crookletch location. However the only son I have found for William so far is another William, when we might have assumed he would be named after William's own father following the naming convention of the time. I haven't come across Andrew as a family name.
Best wishes, Donna.