Probate laws in Missouri?

Needing general information regarding the probate laws in the state of Missouri. My husband's mother passed away on the 18th. Her husband of the last 9 years has basically shut us out and even ignored calls from us. He has not opened the estate, but we were advised by an attorney to file to open the estate and have my husband appointed as the representative of the estate. Any information on this process would be greatly appreciated.