My mother has passed away she had no will. My nephew wants to take over her mortgage I be g the oldest sibling do not want any part of the property.

No.  The estate must first pass through probate, pay your mother's debts and distribute the rest according to the inheritance laws of Florida.  If you are the "oldest sibling," you have siblings who (assuming your father is gone) will also inherit.  You can then gift your interest in the estate to your nephew.  Whether your siblings will also gift their interest is another question.  Whether the mortgagee/lender will foreclose, whether the estate administrator will sell the house, whether there will be money left after paying the debts are additional questions.