With NXT you have a single passphrase(brainwallet) as a login right?
You would actually have to split the passphrase and give the different parts to the family and the layer

I use Nxt, and my Nxt priv. key is on the desk next to me.
A solution to this problem that is safer than my piece of paper is Multisig; you could require both your family, a lawyer, etc. to approve a transaction in order to get have the support them.