My thanks to Peter M. Smith for his research into this this family based on a copy of Alexander's will. Peter has written:

I now believe that the Alexander Mutch who married Helen Roust/Rust in 1799, and who died in 1831 (his will mentions his wife Helen, sons John and Alexander, and daughters Helen (wife of James Elrick), Jean (wife of James Philip), Christian, Ann and Isabel), is also the Alexander Mutch baptised at Newmachar in 1759 (who has been identified in some published trees as the Alexander who died in PEI in 1828). The will begins with the text I Alexander Mutch Farmer in Langhill of Newmachar... In Rob Mutch's website a researcher who looked at the Newmachar PRs reports I found John Mutch son of Alexander of Longhill baptized on March 10, 1755. Alexander was baptized on July 3, 1759. Both baptisms gave the name of the father Alexander in Longhill. A witness for both was Alexander Mutch Sr. [A9].

The following upated information received from Peter 9th December 2003:

I have recently learned from a descendant of the Alexander Mutch whose will I obtained (who was living at Longhill, Newmachar when he wrote his will and who died in 1831 at Philipstown, Old Meldrum), that there is a Memorial Inscription from Old Meldrum, Aberdeenshire, which supports my feeling that he is the Alexander Mutch baptised at Newmachar in 1759:

In memory of ALEXANDER MUTCH late life renter in Philipstown d 1 May 1831 aged 71; his spouse HELEN RUST D. 8 May 1861 aged 87; ...

Peter also provided the following information from the MI list for New Machar:

1856. Erected by JAMES PHILIP farmer Waulkmill, Newmachar in memory of his dau. JEAN d.2 Oct 1855 aged 26; his son GEORGE d.16 Nov 1858 aged 18; His wife JANE MUTCH d.9 May 1866 aged 62. Also of his dau.-in-law MARGARET BURR d.18 June 1860 aged 26. Above JAMES PHILIP d.27 Apr 1872 aged 76. Bottom 2 lines verse.

Daughter Helen is shown on ANESFHS Ancestor Chart 4017.

Peter Smith has provided further details of the families of these children taken from the 1841 census, see this PDF file.

Kit Jocelyn (nee Littlejohn) of Otago, New Zealand has sent the following information about the family of daughter Christian:

Christian Mutch who married Arthur Littlejohn came to New Zealand on the "Timaru" sailed from Greenock 3 June 1877 and arrived at Port Chalmers Otago 6 September 1877.

She lived with her son John at Milton.

Christian (Christina Mutch) Littlejohn died 27 May 1892 at Milton,Otago,and is buried at Fairfax Cemetery Milton aged 81 years.

Their son Arthur was my great grandfather.he came to NZ about 1869,followed by his brother Alexander about 1870,and about 1874 John Mutch Littlejohn and wife arrived.

The family settled in Milton Otago.

Arthur married 30 July 1874 Dunedin NZ to Ann Carr.
Arthur died 26 May 1923 Milton 82 years and is buried at Fairfax Cemetery
Ann born 1843 Fetteresso died 28 May 1935 at Milton 93 yrs buried Fairfax Cemetery.They had 6 children.

Alexander married 30 July 1874 Dunedin NZ to Margaret Fraser
Alexander died 2 August 1919 at Dunedin Hospital 83 years and is buried at Timaru Cemetery.
Margaret born 1836 Skene and died 2 August 1907 at Timaru,South Canterbury and is buried at the Timaru Cemetery,she was 70 years.

John Mutch Littlejohn married 10 October 1874 Upper Rannieshill Mary Jane Godsman,daughter of George Godsman and Ann Margaret Tod. 13 children
John died 13 June 1931 at Dunedin and is buried at Fairfax Cemetery.
Mary Jane died 22 December 1928 at Milton buried at Fairfax Cemetery.She was born 20 October 1851 Murcar Farm,Old Machar.

Ann Carr and Margaret Fraser arrived on the :Mhairi Bhan" 28 July 1874 at Port Chalmers NZ.

Kit also provided the following additional information about Christian's family:

Arthur Littlejohn born 6 Aug 1804 Fintray,died 17 July 1865 Longcroft,Straloch. His parents were Alexander Littlejohn and Isabella Murray.

Arthur and Christian also had a daughter Hellen born 20 October 1834 Old Meldrum,she married William Mackie 27 November 1857 New Machar. William Mackie from Overton Farm,Fyvie.They had about 6 children.?? Hellen or Ellen as she is in the family bible died 15 January 1921.

Deborah Landrebe also from New Zealand has sent the following information about the family of daughter Christian:

My 3rd Great Grandmother Christian Mutch Emigrated to New Zealand aboard the Ship "The Timaru" arriving at Port Chalmers, Dunedin 6th September 1877. Her Three sons had already settled here in NZ, Christian lived with them at Milton, a small town located 50 kilometres south of Dunedin in Otago.

Christian died 27th May 1892 and is buried at Fairfax Cemetery Milton with her son John Mutch Littlejohn, his wife Mary and two of her Grandaughters. Her death notice and obituary can be found on the old newspapers site http://paperspast.natlib.govt.nz/

The Bruce Herald, may 31 1892 page 2. Her obituary says is was the widow of Arthur littlejohn of Straloch and the third daughter of the late Alexander Mutch who was a proprieter of the Estate of phillipstown, old Meldrum.

Her sons all married in 1874; John Mutch Littlejohn to Mary Jane Godsman in New machar (10 children) Alexander and Arthur both married at knox Church, Dunedin on the same day, Alex to Margaret Fraser and Arthur to Ann Carr (5 Children)

Margaret Briggs is descended from daughter Jane/Jean and has provided these details of her family. She wrote:

My line comes from Alexander's daughter Jane/Jean Mutch who married James Philip then their first son James born 1826 who married Helen Cheyne Mavor

Margaret has since provided additional details of this family. You can see the listing she provided here

I found daughter Isobel's marriage on the Diack Family website, which led me to find her marriage record in OPR.

Alexander's wife Helen is recorded as living with daughter Christian in the 1851 census.