We are sorry to hear about your loss and we would would like to express our deepest sympathies.
Unfortunately our privacy policies prohibit us from authorizing non account owners to access another person's account regardless of the circumstances.
We understand that your request is well-intentioned, but unfortunately this is something we won't be able to assist you with. If you have access to your family member's email address that is currently associated to the account, you can request that the password be sent via email.
Below are some instructions that will help you retrieve it.
If you click on the "Log in" link at the top of www.neopets.com, you will see a "Forgot Password?" link inside the pop-up that appears. Please click on that link and enter the username you need the password for. You can also find the "Forgot Password?" link underneath the "Password" field on the login page, located here: http://www.neopets.com/login/index.phtml
If you are not receiving the lost password email, please be sure to check your spam/trash folders, as your email service provider may have filtered it there. Also, please add email@example.com to your email's approved "white list" before requesting the lost password email so that all emails from us get through.
We hope this helps!