England meet South Africa in the final in Yokohama this weekend after producing a stunning display to beat reigning champions New Zealand 19-7.
Eddie Jones' side are favourites to prevail in a match against opponents who narrowly edged out Wales in their semi-final, favouring a kicking game that is in stark contrast to England's free-flowing style.
Vunipola has been a key part of that approach but, despite being on the brink of glory in Japan, he is still getting tips from the family who have travelled to support him and his brother, Mako.
It's #ENGvRSA in the #RWC2019 Final.
— England Rugby (@EnglandRugby) October 27, 2019
"They can be a distraction as well," said the 26-year-old of his visiting loved ones. "You know, [getting them] tickets, trying to give you pointers on how to play rugby.
"My auntie is always great for that. But their support is very important to us. I guess that's all we need at the moment.
"My auntie is trying to tell me how to play number eight and things to my brother as well. So, as good as it is to have them, they can be a distraction."
On the serious business of wrapping up the title, Vunipola knows England must reproduce the levels they showed from the start against the previously all-conquering All Blacks.
"We've set out wanting to be the best in the world and we've got to back up what we did last week," he said. "It can't just be a fluke.
"I think the challenge has been laid out by South Africa and you saw them taking Japan apart and Wales.
"The challenge is going to be up front and so we are going to have to be there, both mentally and physically."
Photo Getty Images Caption: England's Billy Vunipola