elderly father to be taken care of in will

What is the name of your state? FL
my father is in a nursing home and I have power of attorney to handle all of this affairs, medical and financial. I am in the process of making a will. I have no beneficiary to take care of my dad except my wife, and upon her death, a niece and a nephew (his grandchildren). How do I word in a will that upon mine or my wife`s death, that they take responsibility to handle his affairs

You don't. You cannot place a duty to perform on someone in a will. You would be better setting up a trust now for dad's care.

thank you for the information. I do not want to "place a duty to perform" on someone in the will. I am also my dad's personal representative in his will. I was wondering if I could list in my personal will
"that if my personal representative (my wife) is unable or unwilling to serve in my father's matters, then I appoint an alternate personal representative who will be authorized to carry out all provisions of my father's will and pay debts, obligations, etc."

could I word it something like this. I am going to take your suggestion also and see my attorney in a few months about setting up a trust for my dad.

Perhaps if you lived in a state with a moral taxation policy of taxing income than you would not need to be so worried about the very unlikely prospect of dying before your father.

But since you live in Florida the chances are pretty good that he'd just be kicked to the curb and wind up homeless.

Glad you saved all that money on taxes.