My son lives with me in a home that my sister owns via my brothers will. I am helping with bills including the mortgage until we get it ready to sell. My son has paid no rent or contributed towards bills despite being asked to. He has now brought home a girlfriend and now there is drinking, drugging, chaos, yelling,etc. I want to start the process to make him go. What is it and if worse comes to worse, can I put his things outside (do I have to do this part?) change locks when he is gone? Thank you

You must evict him just like any renter ( does not matter if he is not paying rent) he has taken up residence there. So you notify him in writing that he must move out, and if he does not, you evict him in court.

Have you just tried, telling him he has to leave?

It is likely your son is considered a resident and, therefore, must be treated as a tenant with all the rights of one. That means you can't throw his things out, you can't change the locks. This would probably be considered an illegal eviction and open you and your sister to a lawsuit. How long has he lived there? Since this is California, he might be considered a lodger which has special rules on evictions. http://www.dca.ca.gov/publications/landlordbook/whois.shtml

Since your sister owns the property she has to be involved in the process. Any orders to vacate, court filings, etc. must come from her.

The general process is to give him a written vacate notice with a deadline, probably 30 days. If he doesn't leave by then the next step is to go to court for an eviction order.