You can just write the private key in a letter, and seal the letter and gave it to a lawyer who will give it to your children when you die.
there is no way I would trust a lawyer with this, he opens letter and burns it after. No one would ever know!
maybe transfer the crypto-coins into real money or assets to leave as an inheritance?
Again, that's all fine if you know your death is approaching and have time to get your affairs in order, but if you get run over by a bus tomorrow, how are you going to convert your crypto-currency into "real" money (note the quotes, as fiat-money isn't inherently more real than BTC)?