I am a landlord in Ohio. My question is by having my tenants sign a new month to month lease does this void the old one. My dilemma: She has been there for three years with her son, although she has had three boyfriends move in over the years. Now she has a boyfriend with two other kids. The kids aren't there all the time but he is, with access to the house. Good tenants, but what is my action to protect ourselves..
Thanks.

Yes, she can sign a new month to month rental agreement (if that's what you want) or you can evict her (if that is your choice).

What are you attempting to protect yourself from?

Any subsequent lease supercedes any previous one. If you want to protect yourself prepare a lease that provides you protection. It's not clear what you are looking to be protected from.