Backing up ones wallet and passing instructions or information to heir or next of kin is not actually a bad idea and just like you said there are things we can not be sure or certain about because we are just human but the problem is sometimes human being can be unpredictable, though there are some heir or next of kin that no matter what they saw in your wallet they can never move or tempted to eliminate or still what is inside because of the ethics they have but some too even with their ethics they will look for a way to do something funny. However, the fact still remains that if you didn't pass the necessary information or instructions to the heir or next of kin and peradventure something bad happens to the investor off course the asset will be loss but it will be better if an heir take it than for it to waste.
There is some level of caution someone should exert when dispensing information about his Assets in general. Now making reference to my Bitcoin portfolio, I don't think it's wise to let my siblings know the worth of my wallet both the one in the exchange and non-custodial wallet and this is how I did it.
For my exchange(binance) I gave my youngest sister my logins to the account, then I activated two factor authentication which means no one can gain access to it unless authorized by me and In the event of my exit before getting married, my youngest sister who has my details has been instructed in his she can can go ahead to recover my email with my SIM card and have access to the exchange.
For my non-custodial wallet, she knows where it's stored in my house, but she cannot have access to it until I'm no more because I've safeguarded it very well and no one access that environment anyhow. I also trust her not to gain undue access to the seed phrases without my consent.
It's also important that you don't tell much of your family members about your logins, but enlighten them on it's availability with your most trusted person and In the event of your demise, everybody would be involved and follow your direction on sharing formula, so the person with the details cannot achieve everything.
I believe when people know too much about something, they get unduly attached and desperate for it.