You are in NYC and the City is not going to let you turn off electricity or water to someone living in the house once they find out. You have a civil matter on your hands. You have no lease, the guy owns a percentage of the property, you have nothing in writing that would remotely give you the right to shut off the utilities.
You can take it upon yourself to do just that and see what happens. One call to the City hot line and the inspectors will be knocking on your door.

