In most states, upon Divorce the law treats a former spouse as if he or she died before the Testator, i.e. the person making the Will.
But typically the remainder of the Will continues to be effective.
So generally, a former spouse of a Joint Will is treated as deceased and the children named in the Will remain as beneficiaries.
But not always.
The state law where the Testator resided at the time of death may provide a different conclusion.
And if any additional facts exist like the nature of property ownership, other children, etc. the conclusion may be different as well.
For such a complex situation, Standard Legal strongly suggests consulting with an attorney. You can find a local attorney for FREE at the Attorney Find page.