Seems like a neat idea actually. Just be careful on choosing whom to give a piece of the passphrase as it will be valuable in times of need. If in case one part of the passphrase is lost, creating the whole passphrase and safekeeping it would save you and your family in case one part was lost.
thats why you use static data, like a social security number or date of birth. so its readily available.. but without having to actually write down the data itself.
-snip-
But what if, say for example, all of the wielders of the passphrase were caught in an accident and you have no copy of the whole phrase, that means you already lose the funds if ever, so keeping one 'just in case..' would always come in handy, at least on how I view it.
as i said.. you dont hand out the splits of the passphrase to the person on post-it notes....
you use a piece of data that is significant to that person. and only mention that persons name in your will.... that is it
that way the lawyer wont even know the passphrase when drawing up the will as its not wrote anywhere. only hints are provided. that will only be pieced together when all 4 family members are at the reading of the will. and are people that collectively know each other to piece it together (should one die) and then under the supervision of the lawyer reading the will he will ensure it is administered correctly.
for instance until the will is read the 4 relatives have no clue if its their social security number, date of birth, or middle name which is the split.. they wont find out the hint until your death. and then only while infront of the lawyer will that hint be revealed. and if there are only 3 out of the 4 people alive. they under supervision of the lawyer will know the missing person to fill in that hinted info. to then split the funds as deemed moral