I have heard you can access the chapel early, and have seen mentions of it in this forum, however I can not find where one books for such an event. I've tried Viator and they have "skip the line", and I tried direct with the Vatican but could not find what I was looking for. We are 4 persons and are willing to do a private tour. Can someone please advise?
Walks of Italy offers this as do a few other tour companies
https://www.walksofitaly.com/vatican-tours/pristine-sistine-chapel-tour/
Book with the actual tour company not Viator which is a third party reseller
A forum search will bring up other tour recommendations
Beware of sites that look official but say “by Walker” in header-they are a scam