The problem of seeds is obviously crucial. Can we imagine being the one and only person who knows what to do with these 12/24 words? How to keep them safe, but also how to pass them on to heirs or friends (so that they know what to do with them?). Informing others while preserving your own security can be a real challenge in some countries.
And then there's betrayal, divorce etc...
What are the solutions?
You just have to tell someone that you trust and tell about it, there is no use keeping it out secretly forever and your loved ones or children that are suppose to benefit from the wealth don’t know about it. You can also make it in such a way that they can only access the seedphrase only when you’re no more. The issue of betrayal and divorce you made mention of are important things to look out for, so it is better one takes their time and find a solution to this before concluding on who to know or delicate an information so important like this into their notice.