3. Perhaps the most controversial part. I will write my 24 word seed phrase with "archival" permanent invisible ink in a book. I will duplicate this in another book and keep the second book in a safety deposit box or in a P.O. Box at the post office. (I will check from time-to-time the longevity of the ink.)
Why are you like to handover your seed like post office box? I know you will secure it by something else. But do you know that no system is safe? Seems you are too much worried about your seed how to store it. Why not make it simple? Store your seed on multiple safe places. Even 1 would burn another will survive. Safe zone means under your control, it might on your house or some other places. If you think your home wouldn't safe then think what will happen if you die ? So there is no guaranty actually. That's life, and I has no guarantee. So it would be nice solution, write your seed on multiple good paper and store it on multiple safe place and check occasionally if your seed is fine.