This is a hard question. I tried my best to encrypt everything and deploy best practices everyhwere. On the other hand, this is my first project in Go and I feel like an impostor giving out this project to the world made with my skills. And I will compile with law enforcement if they ever point a gun at my head and ask me to give them your data. This leads us to the next topic:

How I would store it:

Write a nice, not incriminating text message (remember, I will compile before being killed) to the recipients of the will. Greet them from the afterlife, write something about music or so. Everything sensible gets stored in a .zip file attached as an attachment, encrypted with at least AES-256 (!) and a secure password (!!!).

Then, I would give the password to the recipients via a secure channel (preferably a carrier pigeon, because they are most definitely not government drones), and tell them not to lose it.

This way, no one can access the sensible content, no matter what happens.