Many thanks for the suggestions and help. I've been trying to get this straight in my mind, here is my attempt.
Family Group 1As Isobel identifies, a David Clark b about 1847 is with his family (father Alexander a boot/shoemaker born in Scotland) in the 1851 Census (2183/25/42) and 1861 Census (2680/16/36), but not in 1871 (3780/135/36).
David appears to have married Mary Ellen Squire on 17 Jan 1870; consistent address and father with the above census records - Alexander's occupation given as Toolmaker (
https://www.familysearch.org/ark:/61903/3:1:3QS7-896P-KDRK - thank you Blue70)
David's occupation is given as a CoachSmith.
David and Mary had a son, Alexander, baptised 21 Dec 1870 in Everton; father David, a Coachmaker; St. Peter's Church, Liverpool (thank you Isobel)
Alexander may have died before the 1871 census (thank you heywood)
In the 1871 census there is a David and Mary Clark with a 24m daughter (i.e. born pre-marriage of David Clark and Mary Squire). We are uncertain of who the daughter is, Ada and Louise Squire appear to be with mother Charlotte in 1871 (3824/36/18). Possibly Isabella Ritchie Squire (b 1869).
The fate of this daughter and Mary is currently unknown.
David's age is consistent with the David in family group 2, and his Scottish Ancestry with family stories.
Family Group 2A David Clark married Caroline Louisa Gee and had the family as detailed at the start of this thread.
Freebmd doesn't appear to show the marriage record between the two parties (thank you BumbleB)
David died aged 53 Q2 1901 8b 312 (thank you Carole)
Family Group 3A Caroline Louisa Gee married Alexander Clark in a civil marriage in 1909 (as shown at
www.cheshirebmd.org.uk, thank you Carole)
As Chempat describes, they appear in the 1911 census, age 46 and 36 respectively (
https://www.familysearch.org/ark:/61903/1:1:XW3P-RHF) The children are consistent (name, age) with Caroline's younger children from family group 2.
Carole shows the 1891 Census only has two Alexander Clarks in Liverpool (excluding the one born to David & Caroline)
1878, parents John W & Grace
1879, parents Cummings and Martha
The second Alexander appears to be related to David Clark from family group 1. Cummings Clark married Martha Steward 30 Jan 1876 (Liverpool Registers after Ancestry), father Alexander Clark, Tool maker (i.e. same occupation as shown for David & Mary Ellen Squires). Cummings and Martha had a son in Q1 1879 (8b 416). Therefore Cumming's son Alexander is David's nephew (if I've followed Isobel's logic)
Caroline L Clark died Q4 1838, age 76; Wallasey 8a 696 (thank you heywood)
Please do let me know if I have got any of that wrong, and apologies if I missed anyone. Thank you all very much for your help. This is certainly great progress.
The ages of Caroline and Alexander in 1911 are not consistent with the other records, but as chempat suggests, that may be due to the husband being younger.
So I think I will purchase the 1909 certificate as a christmas present to myself and hope to find evidence to support Caroline in family group 3 being the same Caroline as in family groups 2, and also that Alexander is the son of Cummings Clark and therefore the nephew of the David in family group 1. Caroline's father's name in the marriage may also support her being the daughter of James Gee and Julie Ann Howard as identified by Carole.
If there was a marriage record for David and Caroline then the father's names and occupations may support/refute grouping these families together. I guess I was hoping there may be a source I hadn't searched, but perhaps I'm looking for something that doesn't exist.
I note David's signature when marrying Mary Ellen has a distinctive D, so if I could find a signature for the David who is with Caroline, and it is similar, then that may also support them being the same David.
Thanks again for all the help.