
In such situations, it is possible to buy special life insurance (sometimes called "survivorship life" or "second-to-die insurance") which will pay only after both spouses die.
Assuming that the Jones family has adequate cash to buy such a policy, they must be extremely careful to avoid giving Mr. or Mrs. Jones any "incidents of ownership" over the policy. (If they buy a $5 million life insurance policy, and the policy proceeds were included in the estate, then the total estate would be $15 million and the tax would be more than $7.5 million, still leaving a cash shortfall.)
The obvious solution is for the Jones' children to buy the insurance on their parents' lives, or for Mr. and Mrs. Jones (or their children) to set up a special life insurance trust.