If one spouse deceased, how can estate enforce decree on other spouse?

From what you've written, the $333,000 sounds like an established property right of your father's, under the divorce decree, and that right now belongs to the estate.  So the personal representative (executor/administrator) should now file a motion in the family court, in the name of the estate, to enforce the decree, just as your father could have done if he were still alive.  The legal fees for this would be an entirely proper estate expense.

A court order isn't negotiable, and it can't be amended later at the whim of a person subject to the order.  The ex-wife can oppose the motion, and she can cross-move for the decree to be amended so she doesn't have to pay as much, but she'll have to come up with a legally sound reason for that if she expects to get anywhere, and I think that's unlikely.