All accounts lead to some couple of emails where you can set things up and that email leads to (one time pin) OTP on your handset. You need to share those credentials and ultimately before changing any passwords you get sms alerts (better to go for double authentication).
You also need to explain how to change the passwords if one forgets....
Explain these things to some of your family you trust, tell them little bit about the domains (it might take little sessions with someone you trust in your family).
You got to trust someone (at least) though....