I have a customer that has recently been put in the nursing home, his wife has presented us with Letters of Guardianship. How does this pertain to his accounts? She is only listed as beneficiary to his accounts, but is listed as a co-owner of a safety deposit box. I just do not really know if this paper has any say over his banking business.

You should have received a certified copy of the court order appointing the spouse to be guardian. The order will outline what the guardian can do and the order may be quite broad. Your account agreement should also address court orders and your response to those orders.

If the court has appointed his wife as guardian of his person and estate (property), it means that he can no longer transact business in the accounts or access the box. She can do so in his place, as guardian. You'll have to read the appointment document to determine the status of the guardian. If she only is guardian of his person, she doesn't get access to the accounts or safe deposit box in that capacity (she can access the box in her own right, though, as co-lessee). If you can't decipher the appointment, ask someone with familiarity with such documents -- your trust department or an attorney -- to check it out.

In this context, the word "estate" refers to the individuals property. It doesn't mean that the guardianship kicks in when he dies.

The guardianship (and the guardian's authority) ends with his death.