John and Charles were born in Wales in the last decade of the 18th century. Later they would claim to have discovered in 1811 that they were descended from the Stuart kings, and on their 1871 census entry they gave Versailles as their birthplace. They moved to live in Scotland and changed their Allen surname to the more Scottish spelling Allan, then to Hay Allan, and Hay. Their father John Carter Allen had Hay ancestry, and was said to have been related to the Earl of Erroll.
In 1840 John would publish a Genealogical table of the Hays. The date of their arrival in Scotland is unclear, but they are known to have been there in 1822. This is the year John published The bridal of Caölchairn and other poems under the name John Hay Allan. Another edition was published, also in 1822, giving the author's name as Walter Scott. This is now in the British Library's category of "doubtful and supposititious works".
In 1829 they failed to persuade Sir Walter Scott of the authenticity of a document they said was a copy of a "15th century" manuscript about clan tartans. The brothers liked to wear Highland dress themselves, apparently "in all the extravagance of which the Highland costume is capable". In the 1830s they moved to Eilean Aigas on the River Beauly in Inverness-shire, to a hunting lodge granted them by the Earl of Lovat. Here they "held court" and surrounded themselves with royal paraphernalia: pennants, seals, even thrones. During their time here, they adopted the final version of their names", using the surname 'Stuart', and became practising Catholics. (The Stuarts and their supporters, the Jacobites, were Roman Catholic.) They got to know various important Highland chiefs and noble patrons, one of whom was the Earl of Moray, and pursued the aristocratic pastime of deer-hunting. This was the inspiration for Lay of the Deer Forest. With sketches of olden and modern deer-hunting (1848).
They published the Vestiarium Scoticum in 1842. This was followed, in 1844, with a broader "study" of medieval highland Scotland which included the ideas from 1842: The Costume of the Clans. With observations upon the literature, arts, manufactures and commerce of the Highlands and Western Isles during the middle ages; and the influence of the sixteenth, seventeenth and eighteenth centuries upon their present condition. This involved "immense scholarship" , but the historian Trevor-Roper is just one of many who consider it full of "fantasy" and "forgery".
In 1847 their claims to royal blood were set out by implication in a work of historical fiction: Tales of the Century: or Sketches of the romance of history between the years 1746 and 1846. After this, a strong attack on them published in the Quarterly Review in 1847 caused severe damage to their reputation. John responded with A reply to the quarterly review upon the Vestiarium Scoticum in 1848 but the brothers soon were forced to move away from Scotland, to live with relations in Prague and Pressburg. In the latter 1860's they lived together in reduced circumstances after the death of Charles's wife and continued to occupy themselves with research, being famous figures in the British Library, using pens embellished with gold coronets, and wearing Highland dress or military tunics. Only after death did they return to Scotland, to be buried in Eskadale.
John and Charles were the sons of Naval Officer Thomas Hay Allen and his wife Catherine, daughter of the clergyman and antiquary Owen Manning who was vicar of Godalming for many years. Thomas and Catherine also had a daughter Matilda. John, Charles and Matilda were all born in Wales, and after the early death of their mother, Thomas remarried Ann Salmon and had five further children, many of which took assumed names. After this date Thomas is a shady and elusive character. He may have invested poorly and have been plagued by debts, which would explain his living abroad, and his use of an assumed name. He died in Clerkenwell in 1852.
John married an heiress Georgiana Kendall in 1845 but had no children. Charles married Anna Beresford in 1822 and had three daughters and a son, named Charles Edward Louis Casimir Stuart(1824–1882). This son, the first to be christened a Stuart, married Lady Alice Hay, daughter of the 17th Earl of Erroll, but they had no children. Two of his sisters died without issue, one becoming a nun. His sister Louisa Sobieska (c1827 - 1897) had a son with her husband Edouard von Platt who served in the Austrian imperial bodyguard. There is no-one who could continue the "Stuart" brothers' claims to royal ancestry through the direct male line, although descendants remain.
The Allen/Stuart brothers implied that their grandfather, Admiral John Carter Allen, was merely foster father to Thomas, whose "true" father was Charles Edward Stuart, or Bonnie Prince Charlie.
Sobieski is the surname of John Sobieski, the Polish king, whose granddaughter Clementina (Maria Klementyna Sobieska) married a Stuart: the "Old Pretender", Prince James Francis Edward. Their eldest son was Charles Edward Stuart, the "Young Pretender", and the Allen brothers claimed him as their "true" grandfather.
John also called himself John Sobieski Stolberg Stuart. Princess Louise of Stolberg-Gedern was married to Bonnie Prince Charlie and is sometimes called the Countess of Albany. John, and others in the family, started to use the title Count d'Albanie, which "passed" to Charles on John's death at 52 Stanley Street (now Alderney Street), Pimlico, London in 1872. Charles died on board a steamer on a trip to France in 1880. His son inherited the title and is buried as the Count d'Albanie.