Basic "I'm not too worried about it" level of security: stick it on a webserver using .htaccess to demand a password. Make that password halfway decent.
Better option: export to PDF by either exporting to HTML or latex and then using that system's PDF export. Keep both PDF and original in a folder on Google drive or Dropbox that is shared only with those who need access. (No password needed at all so you won't have someone compromising you with a crap password)
Best option: same thing but store those files in a respected password manager like 1password or keepass. Train your family to use the password manager. Use it as a vault for all sorts of "just in case, they should know" info.
In theory, you could even automate things to work on a deadman's switch. Have a system that pings you via email, SMS, or another communications mechanism weekly. If you don't respond within a few days, it automatically shares the aforementioned files using gdrive, Dropbox, 1password, etc (not email though - email is not secure)