Upvote:6
You should probably consult an immigration lawyer.
This not straightforward and a professional opinion is a good idea.
My belief was originally that you would require a work visa to be a tour manager. You are actually performing work, looking after customers, while in the US. However the reply you quote in comments to an enquiry to the US embassy leads me to doubt that view. However I would still make use of a US immigration lawyer. The downside of working illegal in the US, even if you do it accidentally, are quite large.
You might be able to make a case that only you were capable of acting as tour manager, but that is definitely a question for a lawyer.
Incidentally it makes no difference if you go for Visa Waiver Program (sometimes called ESTA) of business visa - what you are allowed to do is the same in each case.