I encurage everybody to engrave their secret in steel or copper. It will survive a house fire and it is not so easy to lose as a piece of paper. On the other hand, the secret should be divided into two separate pieces stored in two secret locations (with your family members knowing exactly where) in case one is stolen.
I think you meant 2 sets of keys divided into 2 pieces each (4 pieces total) can protect you against theft of 1 piece.
It does seem as quite reliable, but there is the posibility of a trusted party using the coins without youre agreement, like before you loose access to youre account. Might be a problem in many cases.
This whole proces implies a lot of trust factor so I think that trust factor is the one that should be minimized or idealy deleted from the equation.
I updated the first post according to your responses.
thanks, yes in principle I thought about 4 pieces total. But look, if the secret you want to safeguard is a backup wordlist for your hardware wallet, then it is perfectly enough to have it divided into 2 pieces of steel with engraved information and have a working hardware wallet device as pieces number 3 and 4.
And you are absolutely right about the trust factor. But again, you could store one of the pieces in a safe and have a code for your safe deposited with your will in a sealed envelope with your lawyer. That way, neither your family nor the lawyer has all the info required.
Options are unlimited. The important thing is to have it thought-over really well and make sure, that your family is aware about your scheme.