Generally speaking difficult to say it might or might not have an impact to your application.
In the best case (!) it might not have an impact - McKinsey is rather strict on personal ties, especially for the more senior folks when trying to get new potential hires into the firm. However, if it's in a different geographical region or for another specific practice, it might still be possible though.
In the worst case the firm would not hire you - for sure not in the same area and for sure not having your relative interviewing you.
Summary: Not easier, but even the other way around!
Hope that helps - if so, please be so kind to give it a thumbs-up with the green upvote button below!