Such laws vary widely from state to state, and the tax aspect changes almost daily. You would be very unwise to depend on advice received on the internet.
My advice is to pony up the one hundred dollars or so a lawyer admitted to practice in Missouri will charge for an initial consultation. The local bar association can give you the names of some lawyers who specialize in that area. Another way to find a good specialist in this area is ask the trust department at a bank who they recommend. Inheritance taxes are very complicated and many lawyers know almost nothing about them. Still another way would be to ask a local CPA who you trust for a recommendation. Do not listen to legal advice from insurance agents, accountants, real estate agents, and bankers, all of whom think they know more than they do.