Both sister share a love of designer gear from labels such as Chloe, Gucci and Christian Louboutin and have been treated to trinkets such as Rolex watches by their generous brother.
Hairdresser Erin, 34, a mother-of-two is responsible for Conor's man infamous man bun, telling the Sunday World: 'Everyone loves Conor's hair and so many men want it. It's so funny.
"It's great to be able to express my creativity through him. Conor is very stylish, always has been. It runs in our family."
Erin is currently taking a break from her second career as a bikini and fitness model but said that the rigours of training brought her and Conor closer together.
"Whenever I was low Conor was on the other end of the phone," she explained. "I remember him saying: "No-one realises what it's like until they've done it themselves." We forged this mutual respect that I suppose we never had before."
She's a regular fixture at her brother's fights and is even credited with introducing him to Rhonda Byrne's book, The Secret, which inspired him to embrace the power of positive thinking.
The Notorious has repaid his sister's loyalty by treating her to gifts such as a Louis Vuitton handbag and a swanky white BMW.
Younger sister Aoife, 30, also joined Erin in Sin City at the weekend, travelling to Vegas on a private jet.
Aoife works for a mini digger hire company in Dublin and married husband Mark Elliot last New Year before jetting to The Maldives on honeymoon.
