If you are not w2 they can’t dictate when and how you work. You are the consultant and it’s within your rights to tell them when they are doing it wrong and to charge per person workshop fees for any meeting over top level management headcount.

Especially if you are working with multiple clients, your time is just as important as theirs. Remind them that they have your undivided attention for one hour at a time and to be prepared to move quickly through everything they need to discuss with you. Otherwise they pay for each additional hour. However, you should be able to get through everything if you plan out exactly what will be discussed each session.

Focus on specifics. Calculate the hourly salary of each attendee and let them know what holding a group of that size costs the company. Emphasize efficiency and cost savings of smaller and shorter meetings.

It was actually funny, but I did in a way where I said I felt sad that my clients didn't get my full attention and I posed it as having no other choice. If you're diplomatic and kind it should be seen as someone concerned with their workload. :)

This is absolutely ridiculous, I was at a place like this until I told them I would charge OT for the work I could not get done within working hours due to meetings. After that, each meeting had an agenda and was 45 mins max.