thats why OP said split it..
EG
lets say you know the social security numbers of your spouse and 3 kids
wife 077-99-0099
kidA 087-96-3021
kidB 097-59-1239
kidC 107-98-5868
now without telling them... you make a passphrase using those 4 SS numbers
077990099087963021097591239107985868
you then add on a secret word
077990099087963021097591239107985868hullabaloo
now this is what you write in your will
"dear wife. my savings are locked into bitcoin using you, and our 3 kids SS numbers followed by the safe word we agreed on when having rough sex"
that way even the lawyers wont know it
Unless they bug your bedroom or wherever you would use the safe word for rough sex