Thanks to all who have contributed so far.
maddys52 and heywood have provided evidence from the 1841 Census that James and Maria were not born in Berkshire, as the children were; Their origins remain unknown.
Garden genie has mentioned Prince Edward’s long-term partner, Madame de Saint-Laurent. Wikipedia informs us that Recent scholarship (particularly by Mollie Gillen, who was granted access to the Royal Archive at Windsor Castle) has established that no children were born of the 27-year relationship between Prince Edward and Madame de Saint-Laurent….. After the Duke's marriage in 1818 to the Dowager Princess of Leiningen, Madame de Saint-Laurent retreated to Paris where she lived out her days amongst her family and friends. The Prince may have had other mistresses during that relationship. The Australian historian, Mollie Gillen died in 1909, but her book The Prince and His Lady (1970) might be worth reading.
Maddys52 I was unable to find the article on Edwardina of Feb 1837 in The Age but I did find some in other Australian papers of June that year. A Mrs Carey is not mentioned but the article suggests that Edwarina may have been the child of the Princess of Wales and that George the Third gave the lady in question permission to wear the Royal Arms, and to assume, by courtesy, the title of Lady Edwardina Kent.
Ruskie I am not sure if DNA testing will be of much value as Maria is eight or so generations back and I have found finding connections with low percentage matches is a challenge, as many people don’t publish much in the way of a family tree. Furthermore, as you say, the royal descendants concerned may not have had DNA tests. Nevertheless, I will suggest to my granddaughter-in-law and her mother that they have (at least) autosomal DNA testing.
I agree the photo of Sarah is of good quality and in view of your comment as to not resembling QV, I asked my wife to have a look. She thinks there is some semblance and also even slightly (the nose) to Prince Edward.
Little Nell I agree, the hair style and dress is most likely 1850s to 1880s. Newer hair styles came in within that period but older people may have stuck with the older style. The photo is more likely to be Sarah’s than Maria’s.
rosie99 Surely, that is Maria’s marriage.
I have found a profile of Maria Cross (1803-1848) on geni.com containing the statement Records Blanked Out By Queen Victoria’s mother Cross. I will start a new discussion on that platform, seeking evidence of parentage.
Your help is much appreciated.