Encrypt your package using a fresh private key. Send the package to the will handler (such as PassMyWill), but not the key. Send the key to all the will recipients.
Upon the execution of your will, your recipients get the package that they can already open with their key.
The trick becomes to keep the package opaque to the will handler, and to keep the recipients from gaining access to the package prematurely.
Then you could nominate some family members, friends, significant other, such that some minimum number of them were required to collaborate to decrypt the files.
Encrypt your package using a fresh private key. Send the package to the will handler (such as PassMyWill), but not the key. Send the key to all the will recipients.
Upon the execution of your will, your recipients get the package that they can already open with their key.
The trick becomes to keep the package opaque to the will handler, and to keep the recipients from gaining access to the package prematurely.