Leave the private key to your lawyer. This would seem the most obvious route, because the lawyer already has access to your estate and takes care of it after your death. You can leave your private key encrypted with one lawyer and leave the passphrase to another lawyer, that don't know of each other so that after you pass away your family receives the private key and the passphrase to decrypt it. In the event of your death, the two lawyers will hand over their part of the inheritance to your family and they could decrypt the private key using the passphrase.
But how do you handle multiple wallets and addresses? I don't store all my bitcoins in one wallet or one address. I would have to leave the private keys and passphrases to every one of them and update them as time passes and I add more and more wallets and addresses.
Use a Google account and setup the "Inactive Account Manager". Set it for a period of inactivity of say 6 months ... then after that period passes without you logging in, access / information is sent to a nominated person of your choosing.
You can then store the documents inside Google Drive. As to how you store the files, they could be plain text or a zip/encrypted file. You can also store wallets there ... you can leave instructions on how to use etc.
If your'e extra paranoid, you can encrypt the files before they go onto Drive, just make sure you have instructions on how to decrypt them and make sure you test it.
Just remember no-one should be accessing your Google account or know the password.
The password should be completely unique with 2 factor authentication enabled on it.