When a person dies and leaves money in an active bank account you can only withdraw money from a deceased person's bank account if it has gone through probate and you were granted permission legally to withdraw money from the deceased persons bank account.
Or if you were listed as an account holder such as a joint account holder of the bank account and then you could withdraw the money from the deceased persons bank account.
However you cannot simply just go to the bank or write checks from the deceased persons bank account without permission because that would be illegal.
Unless the deceased person has signed into a will and or gave permission to the bank to allow you to withdraw money from the deceased persons bank account after they have died.
Withdrawing someone's money from their bank account when they are deceased is illegal and the bank will likely not even let you withdraw money from the account unless you have gone through probate.