Our Daily Bleg: How to Fairly Divide an Estate?

A while back, we ran a bleg in which a reader needed help dividing up a loved one’s furniture and other property. Now a reader named M. writes with a trickier and more philosophical estate-dividing problem:

(Photo: Jack Hollingsworth)

My grandmother is 93 and in decent health.  She has 4 biological children, 10 grandchildren, 23 great-grandchildren and a great-great-grandchild is possible (the oldest great-grandchild is married.) She has a decent amount of assets; barring unforeseen circumstances her estate will be a few million dollars.
From the perspective of fairness, one might say the estate should be divided equally between the four children.  From a purely biological perspective, an individual wants to see that his or her genetics be passed on to future generations. In our case, while one of the children produced two grandchildren who in turn have only one of the great-grandchildren, another child produced 5 grandchildren and they in turn 10 of the great-grandchildren.
Is there a formula for dividing an estate like this that balance the equality of each child with recognizing the value of the passing on of genetics to the deeper generations?

Call me naive, but I’ve never considered gene-passing one of the factors to consider in dividing an estate. I’m sure M. would love to hear from people who’ve had experience (successful or otherwise) in a situation like this, whether from the inheritance side or the legal/accounting/consultant side.