We'll be in Milan on a first Sunday of the month. This is from the Cenacolo Vinciano website:
"In addition, on Free Sundays or other free admission days, groups will not be accepted, nor will it be possible to use services such as guided tours and workshops. It is also prohibited to conduct professional guided tours."
So, as i understand it, their own guided tours and outside guided tours are not allowed that day. If I'm misunderstanding this, please let me know. Thanks