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I think having a wallet that has a timelock feature would be the perfect model for them.
if they are already doing that themselves then why do they need to put an additional restriction on themselves for no reason?
the timelock features, as OP mentioned, is most suited for those who have a hard time controlling themselves and want to not be able to spend their coins even if they wanted to. but such restrictions are not good for other people because you can't predict the future and you may need those funds in an emergency.
Good point and indeed, it would be a little bit strange for his family members to use a feature like this, if they can already keep themselves in check with regards to spending.
The chance of doing something wrong and getting stuck with locked coins for longer than they anticipated wouldn't be good exactly.