Can I keep my mother in law from moving in by filing for divorce and then petitioning the court to "lock down" my home?

It's hard to see how filing for divorce would provide the kind of relief you're seeking.

Divorce won't help you in that situation. There is no such thing as "lock down" relief.

There is no "lock down" relief the court would issue. Also, filing for divorce has nothing to do with your mother-in-law moving into your home. You do not advise us if you own the home, if you own the home with your wife, if you lease the home or rent. If you don't want your mother-in-law to move tell your wife. However, it sounds as if your relationship is nearing an end. You really should consult an attorney if you are going to file for a divorce. It is not something self-representation usually leads to a positive outcome.

If there are other facts that you haven't revealed, such as domestic violence, destruction of property, or other issues that would make it unsafe to continue to reside with your spouse (and her mother), there may be a way to obtain exclusive use and occupancy of the marital home or an order of protection. It is a very fact sensitive issue though and you should certainly discuss your particular circumstances with an attorney to explore options. Absent some of the circumstances set forth above though, you won't find the relief you're seeking.