I am not aware that living will can designate guardians and cons

I could be wrong, I am not professional working in that area.

First, living will are known only to set up advanced medical directives.

The problem with incapacity is that the money is still under your name, nobody can spend it without your consent. Without a trust, in most cases your relative has to go to court to apply for a conservatorship, which enables them to access your account. Same with guardian.