His son John inherited two estates from his maternal grandfather (Ynysygerwyn in the Neath Valley and Penllergare, four miles north of Swansea) and, on coming of age, and according to instructions in the Colonel’s will, added the name of Llewelyn to his own. He married Emma Thomasina Talbot, the youngest daughter of Thomas Mansel Talbot and Lady Mary Lucy (née Strangeways) of Margam and Penrice. Significantly, Emma was first cousin to the pioneer photographer Henry Fox Talbot. The newly-weds set up home at Penllergare. During the honeymoon and early days of the marriage, the house underwent considerable alteration and refurbishment and there was much improvement, in design and layout, to the gardens and surrounding parkland.

John and Emma eventually had seven children, six of whom survived into adulthood. The eldest was a daughter Thereza (1834 - 1926), their son and heir was John Talbot (1836 - 1927) known during his young life as ‘Johnny’, then followed Emma Charlotte (1837 - 1928), William (1838 - 1866) called ‘Willy’ by the family, Sybella (1842) who died in infancy, Elinor (1844 - 1887) and Lucy (1846 - 1920).

Although John Dillwyn Llewelyn was a man of independent means, his interests and preoccupations were eclectic. He became actively involved with local affairs. He qualified as a magistrate and was made High Sheriff of the County of Glamorgan. He was a noted philanthropist, giving both time and money to many good causes, sitting on committees and acting as benefactor to local schools and hospitals. For his employees who were not accommodated on the estate he had cottages built, (reputedly designed by Emma) near to his newly endowed chapel of ease, later to become St David’s parish church, at Cors Einon. This hamlet surrounding the Old Inn on the crossways eventually became the village of Penllergaer. With his brother Lewis and brother-in-law Matthew Moggridge, in 1843 he became an active participant in aiding Captain Napier and the police to quell a local Rebecca Riot at the Pontardulais toll gate.

John Dillwyn Llewelyn was a committed family man who, though not a prolific diarist like his father, kept the occasional journal, wrote accounts of local events, papers for the RISW, and frequent letters to the family, particularly his wife, when away from home. For his children he wrote and illustrated stories, often of a chivalric nature and set in fictitious but instantly recognisable local places. Throughout his life he was intensely interested in horticulture, botany and arboriculture and the grounds of Penllergare became renowned for their innovative landscape design in the then fashionable picturesque style. He was particularly fond of orchids and had a purpose built orchideous house, possibly the first of its kind in the UK, erected in the walled gardens.

He was a gifted amateur scientist and a member of the Royal Institution of South Wales. When the British Association for the Advancement of Science met in Swansea in 1848 he met and entertained many of the leading scientists in Britain at Penllergare. His interest in astronomy led to the building of an equatorial observatory (the second only in Wales) adjacent to the mansion. It is perhaps as a photographer that John Dillwyn Llewelyn is now best remembered. Inspired by Henry Fox Talbot, he became enthusiastic, skilful and accomplished and Penllergare was pivotal in providing an infinite variety of subjects for his camera. His last years were plagued by ill health. The asthma he suffered from for most of his life grew worse. He and Emma went to live in London, eventually buying Atherton Grange in Wimbledon in 1879. It was here that Emma died in 1881 and John survived her by only sixteen months, dying in 1882. Both in turn were brought back to Wales and buried in the churchyard at Penllergare.

John Talbot Dillwyn Llewelyn (1836 - 1927) succeeded his father at Penllergare. He was born at Sketty Hall where his parents were staying while alterations were taking place at home. He was educated at Eton and Christchurch, Oxford. He married Caroline Julia Hicks Beach (the daughter of Sir Michael Hicks Beach) and together they lived at Ynysygerwn until his parents retired to London. He proved to be a worthy successor to his father by enhancing and consolidating the horticultural splendours of the Penllergare gardens whose heyday coincided with his being Vice-President of the Royal Horticultural Society. He was a well-respected landowner and squire, noted philanthropist, a politician (M.P. for Swansea 1895 - 1900) and keen sportsman. He was a founder member and first chairman of Glamorgan Cricket Club and was made a baronet in 1890.