When a marriage contract includes more than 2 people, isn't there a possibility of abuse through incorporation?

If I'm married and the wife dies, the contract is ended but for tax purposes I can "inherit" the wife's possessions for free. When I kick it, then the estate is taxed.

If I'm married to 3 wives, and one goes, what happens? Say I add a younger wife, and then we add a younger husband to the mix before I die? Can the marriage contract be extended indefinitely in this manner?