I prefer keeping custody of my seed phrases myself, and only a trusted family member knows where it is but cannot access it easily. If I'm gone or something, the family member can have full access to it.
The safest way is to only give them instructions how to access seed phrases but they wouldn’t get the whole instructions while I still am alive. Maybe a lawyer will hold the last key piece of the instructions so that he can deliver it to my family when I am gone.
In the meantime, completely entrusting your seed phrases to someone even if they are a family member seems risky still. You never know what a person can be when money is involved.
Many people can do things outside their morality in times of need. That is why it is better to keep their wealth to themselves. But everyone must have a trusted person to whom those seed phrases will be safe if shared. Moreover, a person must find such a trusted person. If he goes to the afterlife, His heirs will be able to enjoy it. One can give an idea of his seed phrase to someone trustworthy, where he can keep it. After his death, they should find it and use it. If something like this can be done, then there will definitely be no mistake. If there is a mistake in choosing a trusted person, then there can definitely be a possibility of losing his assets.