Hello,
I am sorry for your loss.
Like any other company, Microsoft takes user security/privacy very seriously. If you do not have the password or pin, this becomes a legal process, in order for you to obtain access.
Microsoft explains the process here:
In the article above, it provides the information regarding documents you need to gather. In addition, you need court order or subpoena, and you can file accordingly (see the Regional variations section). If you are in the US, you will serve on Microsoft's registered agent (you typically can find that info from your State's state of secretary website or by contacting them).