His sister and half sisters are described as witches:

https://www.independent.ie/life/fairy-tale-lives-or-not-the-truth-about-the-guinness-sisters-sad-turbulent-lives/29700716.html

"The sisters are all witches, lovely ones to be sure, but witches nonetheless" Masquerade suits Daphne's insatiable sartorial appetite, but also her fear of the world. 'Being in disguise, assuming another role, hiding behind a costume, is so easy. Being oneself, now that's always a little more tricky,' she said

t was the 1930s, and Noel Coward was making impish repartee about Maureen Guinness, the middle of the three 'golden Guinness girls' whose parties were as wicked and bizarre as their looks were angelic. No one knew what to make of them.

"The sisters are all witches," said the director John Huston. "Lovely ones to be sure, but witches nonetheless.

Who knows what her third cousin, Daphne Guinness, will write about? Who knows what she is? Fashion is her chosen expression of wealth and outlandish style, but fashionista is too meek a word for the most famous of the heiresses today. She is pixie-like, cosmetically frosted and as thin as an icicle. "I'll eat when I'm dead," she once rasped. Her trademark is a black stripe running through her platinum hair. The daughter of Jonathan, Lord Moyne and Lisney (brother of Desmond Guinness), and a French actress, Daphne grew up in Ireland, England and a monastery in Spain next to Salvador Dali.

Daphne is his half-sister.

Nicky Hilton married James Rothschild who is son of BOTH a Rothschild and the Guinness Family. He's a bridge between the two.