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.