The most useful documents you have for tracing roots in Scotland are the 1860 marriage record for Christiana to Charles Stanley (which names parents), and the 1838 immigration record for the sister Janet.
I have had a look through the index of records again, and suggest you follow up with acquiring the records/documentation through Scotlands People.
https://www.scotlandspeople.gov.ukNote that Parish records appear to be very sparse for Morven in Argyllshire. There are no kirk sessions for Morven, and no burials.
MARRIAGE of Allan McEACHERN to Catherine / Katrine RANKINE about 1809 (no marriage record)
Children born of this marriage (The baptism records may yield additional information)
Janet McEachern born abt 1810 (no baptism record)
Mary McEachern bapt 4 Jan 1813 Morven
Cirsty (Christian) McEachern bapt 26 Nov 1815 Morven
Missing baptisms? A gap of 9 years is unusual.
Male (un-named) McEachern bapt 31 Jan 1824 Morven
John McEachern bapt 24 Oct 1826 Morven
Donald McEachern bapt 8 March 1829 Morven
Possible that wife and mother Catherine Rankine died 1829-1830
(There are no burial records at all for Morven parish)
MARRIAGE - Morven 14 Mar 1832
Alan McEACHERN to Catharine McLACHLAN
This is possibly a second marriage for Alan. You would need to look at the marriage record to see what is indicated.
Children born to second marriage
Anne McEachern 22 Feb 1833 Morven
Hugh McEachern 19 Jan 1835 Morven
I believe that this is the family
in 1841. The son John from the first marriage, and Ann and Hugh from the second marriage. Robert Cameron looks to be a cousin through Allans 2nd wife.
https://www.freecen.org.uk/search_records/64e0ddc6f493fd8e1f317ad0/allan-mceachern-1841-argyllshire-morvern-1791-?locale=en1841 census gives year of birth for Allan McEachern about 1790. He could have been a little older. The ages in this census were rounded to the nearest 5, therefore someobe who was 52 was recorded as 50 - so his year of birth is approx. If he married about 1809-1810, it is more likely he was born abt 1787-1788.
In 1851 census Morven, Lochaline village
Ann McEachern, 17, born Morven, a general servant
Hugh McEachern, 16 born Morven, a general labourer
No sign of Allan or Catherine in Morven in 1851 census.
Ann McEachern married Hector Currie in Morven in 1855. (Her marriage cert. should tell you if her parents are deceased.)
Hugh McEachern married Maggie Millar in 1871 Bonhill.