My mother just died and I know for sure she didn't have a signature on a will. My cousin by marriage said he had a will but I've never seen it

The  Durable Power of Attorney expired with your mother. However, if the bank account was held either as "joint with right of survivorship" or "pay on death," it passes outside the Will on presentation of a death certificate. A Will has no legal effect until a Court admits it to probate (proving).  If it was not signed, it will not be admitted to probate. Hire a probate lawyer who practices in the county in which your mother died to file an application to determine heirship.  Without a valid Will or a signed caregiver agreement stating that you are to be compensated out of the estate, it is unlikely that you will receive more than any of your mother's other children but you will receive something.