I am sorry for your loss, this forum is just a user to user forum, no-one here has any account access, try using the process they provide on this link to try to regain access to that account.
http://support.microsoft.com/en-us/accounts-billing/manage/microsoft-account-sign-in-helper
If that process is not successful, on the link below, Microsoft indicate to gain access to a Microsoft account or associated service after someone has passed on is basically a legal process that must be entered into.